EPA 440/1-74/015
DEVELOPMENT DOCUMENT FOR
PROPOSED BEST TECHNOLOGY AVAILABLE
FOR
MINIMIZING ADVERSE ENVIRONMENTAL IMPACT OF
COOLING WATER INTAKE STRUCTURES
\
5SS2
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
DECEMBER 1973
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Publication Notice
This a development document for proposed effluent limitations
guidelines and new source performance standards. As such, this report
is subject to changes resulting from comments received during the period
of public comments of the proposed regulations. This document in its
final form will be published at the time the regulations for this
industry are promulgated.
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DEVELOPMENT DOCUMENT
for
PROPOSED
BEST TECHNOLOGY AVAILABLE
for
MINIMIZING ADVERSE ENVIPONMENTAL IMPACT
OF COOLING WATER INTAKE STRUCTURES
Russell E. Train
Administrator
Dr. Robert L. Sansom
Assistant Administrator for Air & Water Programs
Allen Cywin, P.E.
Director, Effluent Guidelines Division
Dr. Charles R. Nichols, P.E.
Project Officer
December , 1973
Effluent Guidelines Division
Office of Air and Water Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
6Q6QJ*
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PROTECTION
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EXECUTIVE OVERVIEW
Development Document for Proposed Best Technology Available for
Minimizing Adverse Environmental Impact of Cooling Water Intake
Structures.
Introduction
Water withdrawal for cooling by industrial point sources now amounts to
approximately 70 trillion gallons per year. Steam electric powerplants
withdraw approximately 80% of this, or 60 trillion gallons per year
which is roughly 15% of the total flow of waters in U.S. rivers and
streams. The intake of cooling water by broad categories of industry is
given in Table A. The relative potential significance of average intake
cooling water volumes for establishments within the broad categories is
shown in the table. However, the maximum cooling water volumes for
individual establishments will be dependent on factors such as products,
processes employed, size of plant, degree of recirculation employed in
the cooling water system, etc.
TABLE A
Intake of Cooling Water by Broad
Categories of Industry (Year 1967)
Category
Intake Volume
Billion gal/yr
Steam Electric Powerplants 40,000
Petroleum Refineries
Primary Metals Mfg.
\Chemical Plants
Pulp and Paper Mills
Rubber Mfg.
Wood Products Mfg.
Pood Products Mfg.
'Stone, Clay, & Glass Mfg.
Textile Mills
Leather Mfg.
1,230
3,630
3,530
650
96
52
430
140
24
1
NO. Of
Estab
1,000
260
840
1,130
620
300
190
2,350
590
680
90
Avg. Intake
Billion gal/vr/estab
40
4
4
0,
0,
0,
0.
1.1
0.04
0.01
Adverse environmental impacts that could occur from cooling water
intakes relate to the net damage or destruction of benthos, plankton and
nectonic organisms by external interaction with the industrial cooling
system. Important aspects of the intake which relate to adverse
environmental impact are the intake volume, the number and types of
organisms which interact externally with the intake or which interact
internally with the industrial cooling system, the configuration and
operational characteristics of the intake and plant cooling system, the
thermal characteristics of the cooling system, and the chemicals added
to the cooling system for biological control.
111
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The above impacts are highly site-specific. Therefore, adequate
biological data would be needed in each case to determine the specific
need and control strategy related to minimizing environmental impact of
intake structures.
Applicable Technology
The range of technologies corresponding to the control of the number and
types of organisms which interact externally with the intake is
comprised of two factors - the choice of the location of the intake
relative to the location of the organisms; and the full array of process
modifications including the use of recirculating cooling water systems
employing offstream means to transfer process heat directly to the
atmosphere, to minimize or in some cases eliminate the use of cooling
water. The technology for controlling the number and types of organisms
which interact internally with the cooling system is comprised of one
factor in addition to location and flew volume controls as cited above
for intake interactions, i.e., the degree to which the conriguraticn and
operation of the intake means prevents the entry of these organisms into
the cooling system. The technology for preventing the entry of these
organisms while minimizing damage due to external interactions with the
organisms is diverse, including a multiplicity of physical and behavior
barriers and including various fish bypass and removal systems.
Damage due to internal interactions with process cooling systems relate
to the design and operation of these systems with respect to mechanical,
thermal, and chemical characteristics. For example, the presence of a
cooling tower in a nonrecirculating ccoling system could affect the
amount of organism damage due to the pumping, temperature changes, and
possible chemical additives employed with the tower.
The extent of the known present application of these technologies to
industrial cooling water intakes is extremely limited, and is largely
confined to steam electric powerplants. However, some technologies
applicable to industrial point sources have been applied to irrigation
potentially and other flows.
Costs
The choice of intake location, while a potentially available technology
to some degree for all industrial sources for controlling the number and
types of organisms interaction with the intake, could be more costly
incrementally in the case of relocating an existing intake, than
applying a recirculating cooling system to minimize or eliminate cooling
water flow. In general, the incremental costs associated with caoice of
intake location or application of recirculating cooling systems to
control the number and types of organisms interacting with the intake
would be less for a new source than for a similar existing source.
However, little is known concerning incremental costs since no
IV
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industrial point source, new or existing, is known to have added this
technology (location).
Some information is available concerning the performance and costs of
various intake devices in specific applications both at steam electric
powerplants and elsewhere. However, the reliability of predictions of
performance at one site based on performance at anotaer site is low in
many cases.
No modification of a process cooling system is known to have been made
by any industrial point source to minimize damage due to internal
interactions. However, modifications, such as the incorporation of
helper cooling towers to meet environmentally imposed temperature limits
on discharges from nonrecirculating cooling water systems, have been
made to steam electric powerplants which could have possibly increased
damage to organisms interacting internally with the cooling water
system.
Nonwater Quality Impacts
Energy requirements of available control technologies would be
significant in individual cases, only in relation co the extent that
certain types of recirculating cooling water systems would be employed
to minimize or eliminate the use of cooling water.
Energy requirements and nonwater quality environmental impact of all
other available technologies are not known to be significant.
Best Technoloqy_Ayailablg
Owing to the highly site specific cost versus benefits characteristics
of available technology for minimizing environmental impact of cooling
water intake structures no technology can be presently generally
identified as the best technology available, even within broad
categories of possible application. Within this context, a prerequisite
to the identification of best technology available for any specific site
could be, in some cases, a biological study and associated report to
characterize the type, extent, distribution, and significant overall
environmental relation of all aquatic organisms in the sphere of
influence of the intake, and an evaluation of corresponding available
technologies, in accordance with generalized guidelines to identify the
site specific best technology available for minimizing adverse
environmental impact of cooling water intake structure. Studies of the
type outlined above could have a severe economic impact on certain
relatively small establishments with relatively high cooling water
intake volumes. From a nationwide perspective the costs versus benefits
of full studies corresponding to all establishments with cooling water
intake has not been shown to substantiate the requirements that all such
establishments be required to submit reports of such studies. Further,
in the case that incrementally costly intake structure technology would
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be shown to be required, expenditures beyond the cost of recirculating
cooling water systems would generally not be prudent since that option
would remain to significantly reduce the intake volume of cooling water.
Requirements regarding the application of best technology available for
intake structures could be very costly in the case of small
establishments, point sources facing a later requirement under section
304(b) effluent guidelines to meet thermal limitations reflecting a
recirculating cooling water system, or where the best technology
available for intakes would require relocation of the intake.
Certain general guidelines have been developed for site characterization
and the description of location, design, construction, capacity,
operation and maintenance features of cooling water intake structures to
reflect the best technology available for minimizing environmental
impact. These guidelines and supporting data are presented in the body
of the report.
VI
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CONTENTS
Section Paqe
• i-
I Background ..
II Location _
III Design
IV Construction ,?t-
V Operation and Maintenance
VI Cost Data
VII Conclusions and Recommended Technology
to be Considered in Each Case
VIII Acknowledgements
IX References
X Glossary
Vll
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FIGURES
Number Title
1-1 Schematic Diagrams Typical Intake Structure 3
II-1 Intake Location With Respect to Shoreline 11
II-2 Location of Intake and Outfall - Plant No. 5502 14
II-3 Location of Intake and Outfall - Plant No. 0608 15
II-U Intakes Drawing From Different Water Levels 17
III-1 Loss of Head Through Traveling Water Screens 21
III-2 Intake Velocity vs Fish Count 24
III-3 Mean Cruising Speed for Under Yearlings and 24
Yearling Coho Salmon for Four Levels of
Acclimation
III-I4 Effective Screen Area 26
III-5 Undesirable Intake Well Velocity Profiles 27
III-6 Screen Mesh Size selection 30
III-7 Typical Electric Fish Fence 32
III-8 Air Bubble Screen to Divert Fish from Water Intake 35
III-9 Channel to Test Effectiveness of Air Bubble Screen 35
at North Carolina Fish Hatchery
111-10 Bubble Screen Installation at Plant No. 3608 To 38
Repel Fish from Water Intake
111-11 Louver Diverter - Schematic 41
111-12 Delta Fish Facility Primary Channel System 42
111-13 Test Flume at Plant No. 0618 44
III-1U Intake Structure - Plant No. 0629 To Divert Fish by 45
Louver Screens and Return Them Downstream
111-15 Fish Elevator for Fish Bypass - Plant No. 0629 47
111-16 operation of the Velocity Cap 49
Vlll
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Number Title
111-17 Conventional Vertical Traveling Screen 53
III-18 Conventional Vertical Traveling Screen 54
111-19 Traveling Water Screen 56
111-20 Inclined Plane Screen with Fish Protection 58
111-21 Fixed (Stationary) Screen Detail 60
111-22 Fixed (Stationary) Screens 61
III-22a Perforated Pipe Screen 63
111-23 Double Entry, Single Exit Vertical Traveling Screen 64
111-24 Double Entry, Single Exit Vertical Traveling Screen 65
111-25 Double Entry, Single Exit Vertical Traveling 66
Screen, Open Water Setting
111-26 Single Entrance, Double Exit Vertical Traveling Screen 69
111-27 Single Entry, Double Exit Vertical Traveling Screen 70
111-28 Horizontal Traveling Screen 71
111-29 Mark VII Horizontal Traveling Screen 73
111-30 Adaptation of Horizontal Traveling Screen 75
111-31 Revolving Drum Screen-Vertical Axis 76
111-32 Vertical Axis Revolving Drum Screen 77
111-33 Revolving Drum Screen - Horizontal Axis 79
III-3I4 Fish Bypass Structures 81
111-35 Single Entry Cup Screen 82
111-36 Double Entry Cup Screen 83
111-37 Screen Structure With Double Entry Cup Screening 34
111-38 Double Entry Drum Screen Open Water Setting 86
111-39 Rotating Disc Screen in Operation 87
IX
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Number Title Pa
•3 __
111-40 Fish Basket. Collection System 90
111-41 Modified Vertical Traveling Screen 92
111-42 Shoreline Pump and Screen Structure 94
111-43 Conventional Pump and Screen Structure 95
111-44 Pump and Screen Structure with Skimmer Wall 96
111-45 Pump and Screen Structure with Offshore Inlet 93
111-46 Profile Through Water Intake - Siphon Type 99
111-47 Approach Channel Intake 100
111-48 Screen Location - Channel Intake 101
111-49 Shoreline Intake Structure 103
111-50 Flush Mounted Screens - Modified and 104
Conventional Screen Setting
111-51 Pump and Screen Structure 105
111-52 Pump and Screen Structure 106
111-53 Pier Design considerations 108
111-54 Screen Area Velocity Distribution 109
111-55 Factors Contributing to Poor Flow Distribution no
111-56 Pump/Screen Relationships
111-57 Pump and Screen Structure for Low Intake 113
Velocities
111-58 Effects of Pump Runout 114
111-59 Pump and Screen Structure with ice Control n6
Feature
111-60 Infiltration Bed Intake - Plant No. 4222 118
111-61 Infiltration Bed Intake - Plant No. 5309 120
111-62 Perforated Pipe Intake 121
111-63 Radial Well Intake 122
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Number Title
1J-T-xe Page
III-6U Angled Conventional Traveling screens 124
VI-1 cost of Intake Systems 136
VI-2 Design of Conventional Intake 140
VI-3 Design of Conventional Intake Modified by Design 141
Recommendations
LIST OF TABLES
Number Title
A Intake of Cooling Water by Broad Categories of Industry iii
III-l Fish Maximum Swimming Speeds 23
III-2 Traveling Water Screen Efficiencies 28
III-3 Electric Screen Applications - Summary of Design Data 33
VI-1 Cost of Traveling Water Screens 135
VI-2 Cost of Intake Structures 138
VT-3 Cost Analysis - Implementation of Design Requirements 139
XI
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SECTION I
BACKGROUND
The Federal Water Pollution Control Act Amendents of 1972 state under
"Thermal Discharges," Section 316(b): Any standard established pursuant
to section 301 or section 306 of this Act and applicable to a point
source shall require that the location, design, construction and
capacity of cooling water intake structures reflect the best technology
available for minimizing adverse environmental impact.
This statement allows considerable latitude in its interpretation.
Rather than calling for an explicit control and treatment technology to
be broadly applied as in Section 301, Section 316(b) requires that
intakes shall incorporate "best technology available" in terms of
location, design, construction and capacity. The Act also does not
indicate whether new intakes are to be treated any differently than
existing intakes.
In addition, performance and maintenance are important factors which
should be considered in addition to those itemized in the Act. The term
"capacity" relates to the physical size of an intake, and has been
considered as an integral part of design considerations. Consequently,
this report has been divided into the following sections for location,
design, construction and operation and maintenance.
Since the Act specifies cooling water intake structures, this document
is addressed specifically to these types of intakes. It is evident,
however, that the discussion could apply to many other types of water
intakes; for example, non-cooling water intakes for industrial,
irrigation or domestic water supply. A major feature of a powerplant
intake, as distinguished from many others, is the necessity for
continuous operation. Such a requirement imposes many design criteria
that may not be necessary for other types of intakes. Powerplant
intakes cannot normally be shut down to bypass temporary fish runs, to
clean out silt or to lessen some other seasonal environmental impact.
However, shutdowns may be feasible in some instances as with a nuclear
powerplant scheduling refueling for a predictable critical fish spawning
period.
Intake Structure Definition
From an environmental standpoint, an intake consists of all elements of
a water drawing facility from the point of water inlet to the water
screens. The water screens are the last point in the circuit at which
aquatic life can be recovered. Common usage also often includes the
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circulating and service water pumps, where those pumps are located in
the same structure as the screens. However, these are not strictly a
functional part of the intake, from an environmental standpoint. Figure
1-1 shows two typical intake structures designating those parts which
define the intake for the purposes of this study.
Cooling water intakes for industrial point sources fall into three
general categories according to the magnitude of the water flow and the
physical size of the structures involved.
Circulating Water Intakes - These intakes are for once-through cooling
systems, which are designed to continuously withdraw the entire
circulating water flow. The water is passed through tne condenser and
returned to the water source. The typical water usage for which the
intake for powerplants must be designed is from about 0.03 to 0.1 m3/s
(500 to 1500 gpm) per MW.
Makeup Water Intakes - These intakes provide the water to replace that
lost by evaporation, blowdown and drift from closed cooling systems.
The quantity of water required is commonly 3 to 5% of the circulating
water flow. These intakes are therefore considerably smaller than the
cooling water intakes for once-through systems.
Service Intakes - These intakes provide the water required for essential
cooling systems as in the case of a nuclear powerplant. Here, the water
quantity is small when compared to the circulating water flow, averaging
about 0.002 m3/s (30 gpm) per MW of capacity. The structure will be
quite massive due to the requirements for redundancy of pumping and
screening equipment and the need for both missile and earthquake
protection. From an environmental standpoint, visual impact may be
substantial.
Often service water systems and circulating water systems will be
contained in separate bays at the same intake. Most new intakes will
have this design. Older powerplants, built in a series of steps may
have separate intakes for different functions and may use more than one
water source.
Environmental Impact as Related to Intake Structures
The major impacts caused by cooling water intakes are those affecting
the aquatic ecosystem. The aquatic organisms comprising this ecosystem
may be defined in broad terms as follows:
Benthos - Bottom dwellers are generally small and sessile (non-swimming)
but can include certain large motile species (able to swim). Location
of major populations can be reasonably well defined and therefore
avoided by adoption of appropriate locational guidelines. These species
can be important food chain members.
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Traveling Screens
Trash, Rack
Circulating Water
Pumps
5 Water to Plant
Inlet
Structure
Manual
Fine Screens
Inlet Condui
Canal to Plant
and Circulating
Water Pumps
\\
SCHEMATIC DIAGRAMS TYPICAL INTAKE STRUCTURE
(Point of Water Inlet to the Water Screening Facility)
FIGURE 1-1
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Plankton - Free floating microscopic plants and animals with limited
ability to swim. The location of these species generally are apt to be
rather diffuse throughout the water body and therefore the adoption of
locational measures would not protect these species. However, vertical
movement of some species is controllable leading to the aggregation of
many plankters into layers. Locational measures, sucn as withdrawal of
water from hypolimnetic waters, may serve to protect vulnerable plankton
layers. Plankton are also important food chain organisms.
Nekton - Free swimming organisms (fish). Of major concern in many cases
are egg and larval stages which are small and have limited mobility and
therefore generally considered as plankton. Adult fish of most species
will have the swimming ability to avoid the intake provided they are
stimulated to do so. The location of spawning and nursery areas and
migration paths are frequently definable and therefore should be
reflected in locational measures.
One of the first steps that may be taken in the proper location and
design of a cooling water intake structure from the environmental
standpoint is the designation of the organism(s) to be protected. This
approach has been outlined by the U.S. Atomic Energy commission in
reference 24. This approach requires the determination of the species
present in the area of the intake. A determination of their spatial and
temporal distribution is also required. A judgment may then be made as
to which of the identified species are critical to the ecosystem and
therefore would control the environmental design of the intake
structure. It is sufficient to say at this point that the control
strategy for minimizing environmental impact will be different for
planktonic species than for nektonic species as disucssed below.
Impacts on Aquatic Organisms
Impingement - The entrapment of nektonic species against a screen mesh
by velocity forces across the screen. In general, impingement will be
lethal for most species due to starvation and exhaustion in the screen
well, descaling by screen wash sprays and by asphyxiation due to removal
from water for prolonged periods of time.
Entrainment - The passage of relatively small benthic, planktonic and
the smaller nektonic forms (egg and larval) through the condenser
cooling system. Mortality of these organisms is quite variable and is a
subject of considerable on-going research. Damage can occur from one or
more of the following causes:
- physical impact in the pump and condenser tubing
- pressure changes across the condensers
- thermal shock in the condenser and discharge tunnel
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- chemical toxemia induced by antifouling agents such as chlorine
Entrainment is not an impact of the intake structure but rather an
effect caused by the subsequent condenser cooling water system.
Control_Strategy_fQ£_Ljmiting Impacts on Aquatic Organisms
As indicated above, the control stategy for minimizing environmental
impacts at intake structures will vary with the type of organism
considered. Impingement effects can be significantly influenced by
both the location and design of intake structures. This is because the
spacial and temporal distribution cf nektonic species can be reasonably
well defined by biologic examination, and sensitive areas avoided by
proper location of the intake structure. In addition, the size of some
adult nektonic species is sufficient to allow their impingement on fine
mesh screens. Entrainment effects on the other hand are relatively less
controllable by intake structures. This is because the size of the
species are small and they generally lack significant mobility. The
spacial and temporal distribution of these species is more difficult to
define, which will limit the effectiveness of locational guidelines.
Design strategies will also be generally ineffective for these species
since their small size and lack of swimming ability will prevent them
from being effectively screened on a fine mesh screen.
There are more effective ways to control entrainment effects where
benthic and planktonic organisms are identified as critical design
organisms. One approach would be to limit the volume of cooling water
withdrawn from a source to a small percentage of the makeup water to
that source. This would be a limitation placed on intake capacity
rather than other an intake specification. For new plants this would
mean that the large capacity intakes would be located further downstream
and smaller intakes located upstream. Peterson 16 has made estimates of
the thermal capacity of some of the Nation's larger waterways. This
work could be expanded upon to establish relationships between intake
volume and mean flow. Where existing stations exceeded the recommended
volume, steps would be taken to reduce the intake volume. Implicit in
this approach is that the impact of entrainment effects on a waterbody
is related to the volume of intake flow, i.e., the lower the flow the
lower will be the damage to planktonic and benthic species. The
limiting intake volume is that at which the waterbody is able to
compensate for the damage to entrained organisms.
Another approach would be to design the cooling water system to minimize
the effect on entrained organisms. This approach involves limiting the
temperature, pressure, chemicals added, and time of exposure of the
aquatic species to levels that will insure satisfactory survival of the
design organisms. A considerable amount of research has been done on
the subject of survival of entrained organisms after passage through
condenser cooling water systems. The results of these studies are often
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conflicting. A suggested guideline in this area has been offered by the
National Academy of Engineering,3* which recommended that the condenser
system be designed according to the following formula:
t ( T) > 2000
t = exposure time in seconds
T = temperature rise across the condenser (°C)
This formula implies that higher temperature rises could be tolerated by
most species if the exposure time were kept to a minimum. It is
believed that the experimental data upon which this formula is based was
limited and therefore caution is suggested in the application of this
formula.
It is noted that this approach is directed at the condenser cooling
system and is not applicable for intake structures.
Other Environmental Impacts Related to the Intake Structure
Aesthetic Impact - Where the intake structure and balance of plant are
separated by great distances the intake structure may have an imposing
physical presence. This will be significant in wilderness areas and in
natural and historical preserves. Where plant and intake are located
close together architectural treatment can be applied to create an
attractive appearance.
Noise Impact - The sound level of the large circulating pumps can be
quite high. Current practice in milder climates is to construct these
installations without enclosures. Enclosed intakes would not have
significant sound levels.
Acquisition of Biological Data
Probably the most widely ignored aspect of data collection for intake
structure design is the biological data on the aquatic species to be
protected. Most of the data collected for intake structure design
concerns the hydrological information relative to the water source.
This information consists of data on water currents, sedimentation,
water surface elevations and water quality. In general, relatively
little data on the biological organisms is collected. The design of
intakes should be based on protection of the critical aquatic organisms
as well as the traditional design considerations of adequate flows,
temperatures and debris removal. In addition, it has been noted that
the design criteria for the protection of the aquatic environment will
be significantly different for different species in the water source.
It is therefore necessary that in each case sufficient data must be made
available on the biological community to be protected. The data that
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must be provided in some cases, depending on the severity of the problem
and especialy for new steam electric pcwerplants withdrawing water from
sensitive water bodies, should consist of, as a minimum, the following:
The identification of the major aquatic species in the water source.
This should include estimates of population densities for each species
identified, preferably over several generations to account for
variations which may occur.
- The temporal and spacial distribution of the identified species with
particular emphasis on the location of spawning grounds, migratory
passageway, nursery area, shellfish beds, etc.
- Data on source water temperatures for the full year.
- Documentation of fish swimming capabilities for the species identified
over the temperature ranges anticipated and under test conditions that
simulate as closely as possible the conditions at the intake.
Location of the intake with respect to the seasonal and diurnal
spatial distribution of the identified aquatic species.
The criteria for the biological survey for the development, of this
data is not presented here. There are several excellent publications on
the techniques to be used in the conducting of biological surveys. The
EPA has published guidelines for the conduct of bioligical surveys. 9
The techniques will differ both with the type of organism and the source
of water.
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SECTION II
LOCATION
Introduction
Both the location and design of cooling water intakes can jtiave an effect
on the environment. This section is concerned primarily with intake
location, although it will become evident that location and design are
closely associated in many respects.
"Intake" as previously defined, means the entire intake facility which
may consist of one or more elements including an inlet structure (the
point of water entrance) closed conduits and open channels to a pump
structure or a combined screen and pump structure. "Location" refers to
both the horizontal and vertical placement of the intake with respect to
the local above-water and under-water topography. This section attempts
to answer such questions as: where is the intake to be located with
respect to the shoreline, navigation channels, discharge structures, and
fish spawning areas? Also, from what depths is the water to be drawn?
The discussion is concerned with three locational aspects of the
intake's relation to the environment:
The operation of the intake insofar as its location affects
operational characteristics. Operation will usually result in the
major environmental influence to be expected from any intake
facility.
Construction activities such as dredging, excavation and backfill
for channels, inlet conduits, inlet structures, and pump and screen
structures. The environmental influence may be considerable, but
will normally be temporary if suitably controlled.
. • Aesthetics, the appearance of the intake facility and its
relationship to the surroundings. Both the design and the location
of one or more elements of the intake facility may be dictated in
part by aesthetic considerations.
The most important locational factor influencing the intake design is
the nature of the water source from which the supply is being taken.
Other locational factors which must be considered are the relative
location of the intake structure with respect to the discharge
structure, the vertical location of the intake, the location of the
intake with respect to the balance of the plant and the avoidance of
areas of important biological activity. In all water bodies, the intake
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may be located off-shore, flush with the shoreline or inland with an
approach channel as shown in Figure II-l. The reasons for selection of
a particular orientation with respect to the shoreline are both to
provide the required volume of the coldest available water and to avoid
drafting from biologically sensitive areas.
Water Sources
Fresh Water Rivers
Rivers normally are characterized by unidirectional flow, which eases
the intake design problem. Most large rivers will generally possess
sufficient resistance to recirculation due to the velocity gradient to
permit the siting of both intake and discharge at the shoreline.
Recirculation might present a problem at extremely low flows. The base
of the river intake is generally set at the lowest river bed elevation,
however, it should be set above significant silt accumulations to
prevent silt deposition in the intake. Different locations in streams
have different susceptibilities to silting. The inner sides of river
bends are more susceptible to silting than the outer sides. The top of
the intake is usually set for high flow and flood conditions. The pump
operating deck is usually placed several feet above the flood crest
level. Frequently, large water levels and flow variations can make
river intake structures correspondingly high.
Ice flows and debris loading are also significant for many river
locations as are the maintenance of navigation passages. Rivers will
usually possess minimum temperature stratification when compared to
lakes because of greater vertical and horizontal mixing. Finally, it is
necessary to protect the aquatic life from entrapment in the intake. In
doing this, it is best to locate the diversion structure at the
shoreline and employ the sweeping currents of the river to carry fish
downstream. However, such a structure could trap upstream migrants,
leading them to the intake structure.
Fresh Water Lakes and Reservoirs
The most significant difference between lakes and rivers is the fact
that the former are often stratified with respect to temperature. The
thermal stratification of lakes is a rather complex phenomenon. The
heat balance of a lake depends on ambient air temperature, wind speeds,
the topography of the lake bottom and flows into and out of the lake.
It is clear that a large withdrawal or discharge of cooling water can
significantly affect thermal stratification. The zone of cold water at
the bottom of the lake is called the hypolimnion. The water in the
hypolimnion is relatively low in dissolved oxygen and often high in
nutrients (nitrates, phosphates).
10
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A,
< '\
WATER V.
SOURCE
r
WATER
SOURCE
w
££:
TO POWER PLANT
INLET FLL/SM WITH SHORELINE
I I
|.L
TO POWER PLANT
OFFSHORE INLET
WATER
SOURCE
CANAL
TO
PLANT
OPFN CANAL TO INLET
INTAKE LOCATION WITH RESPECT TO SHORELINE
FIGURE H-l
11
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Lying above the hypolimnion of a stratified lake is a zone of distinctly
warmer water, the epilimnion. The significant features of this zone are
that it is the area from which evaporation takes place; it is the region
into and out of which the natural stream courses flow; it washes the
shoreline or littoral zone which is a region of highly abundant life and
it supports considerable populations of life throughout its extent. The
water in this zone is usually high in dissolved oxygen. Artificial
reservoirs may have poorly defined littoral zones because of drawdown
procedures. While the littoral zone of a reservoir would be attractive
because it does not support as much life, it is of little use to the
intake designer who will find a shoreline intake too often high and dry.
Within the epilimnion is the uppermost zone which is called the photic
zone. The productivity of this zone is a function of the degree of
penetration of sunlight and the presence of necessary nutrients. As
little water as possible should be taken from the epilimnion and the
absolute minimum from the photic zone. Off-shore intakes with multiple
entrance ports appear to have great application in stratified lakes.
Lakes generally do not have the pronounced flushing currents that many
rivers have. Therefore, the possibility of recirculation becomes more
significant. In addition, there is no assistance by current flushing to
wash debris and fish past the intake.
Wind forces provide most of the water level variation, and wave
protection is an important design consideration in intake structures for
lakes. Commercial navigation is generally not as important a factor as
in rivers, since shoreline and dams prevent access to most lakes.
However, recreational use is more prevalent on lakes than in many
rivers. The Great Lakes constitute an important exception to this
generalization regarding navigation.
Estuaries
A number of factors combine to make intake design and location selection
for estuaries the most difficult of all water source types. Flow is two
directional which complicates the design of many screening systems.
Similar to lakes, most estuaries exhibit stratification, although
stratification in estuaries is generally less stable than in lakes.
Water density depends on both water temperature and salinity.
Volumetric fluctuations are greater due to the periodic influx of sea
water. The salt content varies with tidal cycles. Estuaries are often
stratified with respect to salt content, with fresh water tending to
ride above the salt. In areas where cooling water discharge effects are
present, density stratification in potential intake areas is further
complicated by the differing buoyancies of warm and cool water, and
fresh and salt water.
12
-------
Estuaries are frequently major spawning areas for both ocean fish and
shellfish, with wide seasonal variations of biologic activity. The
presence of current reversals can also create severe recirculation
problems. Because of the high salt content and tidal variations which
create periods of high and low water, corrosion becomes much more
significant in intakes designed for estuaries.
Oceans
The most important consideration in the design of ocean intakes is the
storm wave protection system. Viave damping upstream of the screens is
required. There may also be heavy sediment load in the surf area.
Other factors to be considered are littoral drift and shoreline
instability. The littoral zone is highly productive biologically,
although generally not as productive as are estuaries.
Thermal stratification exists but is not as stable as that in lakes
because of the higher degree vertical turbulence in oceans. Navigation
passageways must also be considered.
Intake_Lgcation with Respect, to Plant Discharqg
From the point of view of plant cooling water requirements tne use of
coolest available water is desirable. Accordingly, considerable
attention has normally been given to avoiding the inadvertent
recirculation of warm water discharge back into the intake. From a fish
attraction standpoint, the avoidance of recirculation is also
advantageous. Long experience has shown that many species of fish tend
to congregate in warm water areas, especially in the cooler seasons of
the year. In at least one major nuclear plant, a small amount of
recirculation attracted fish to the intake area in winter. The fish
thus attracted were also lethargic due to the low winter temperatures of
the water and they tended to be carried into the screens.
The technical aspect of the avoidance of recirculation is a subject
beyond the scope of this study. Note, however, that the subject would
involve an analysis of the existing water currents, the stratification
of the warm water and the dilution and dispersion characteristics of the
discharge structure.
There are a number of ways in which recirculation can be avoided. Two
of these are shown in Figures II-2 and II-3. Figure II-2 shows the
location of two intakes and discharges at plant no. 5502. The methods
used at this plant to prevent recirculation is to locate the intake a
considerable distance off-shore and locate the discharge at the
shoreline. Figure II-3 shows the location of the intake and outfall for
plant no. 0608. This plant avoids recirculation by withdrawing water
from one body of water and discharging to another body of water. Other
13
-------
LOCATION OF INTAKE AND OUTFALL - PLANT NO. 5502
FIGURE 'LI~2
14
-------
n
0 .
— 1
z:
o
^
i
LoJ
"i- V--UIXL/L/1
^^^^^nzi
800 FT.
/
'"-•-•
•^^
>
"•' ••
*• ••
^
POWER
PLANT
SCREENWELL
^
L
INTAKE CONDUIT\v
350 FT. ^
INTAKE
MOSS LANDING HARBOR
LOCATION OF INTAKE AND OUTFALL - PLANT NO. 0608
FIGURE H-3
15
-------
ways of avoiding recirculaticn are to separate intake and outfall by a
sufficient distance, the construction of a physical barrier between the
intake and outfall, and the excavation of a channel for the intake or
outfall or both. Prevention of recirculation also requires adequate
vertical separation of intake and discharge. This is importanr in a
stratified water body such as a lake. Vertical separations of between
20 to 60 feet have been used at some locations.
From the standpoint of the effect of recirculation on fish attraction,
it should be noted that proper location of the inlet point both with
regard to site location and water depth, is an important design element
to be considered.
Intake Lo_cation_with__Resggct_to^the_Shprgline
As mentioned above and shown in Figure II-l, there are three basic
orientations of intakes with respect to the shoreline. Tne difference
between them is the relative position of the water inlet with respect to
the shoreline. The intake at the top of the figure has the inlet flush
with the shoreline. This intake may also be called a shoreline intake
or a bankside intake. The middle intake has the inlet located offshore
with a conduit leading to the shore. The offshore inlet may be only a
pipe opening as shown, or may include water screening facilities and
pumps. The third type of intake uses an open channel inlet (generally
excavated) leading to an inland water screening facility. This latter
type of intake may also be referred to as an onshore intake.
Each of these different intake orientations may be used for any type of
water source (river, lake, estuary, or ocean). The flush inlet and the
offshore inlet offer alternate means for withdrawing water in areas
where aquatic population may be minimal. The third scheme (open
channel) may have desirable attributes from an aesthetic point of view,
but often creates a problem due to fish which collect in open channels.
This aspect will be discussed in the design section of this report.
Intake Location with Respect^to Water Depth
From the biological standpoint, the depth at which water is taken can
be a major factor regarding damage to aquatic organisms. In some
locations, it may be desirable to draw surface water only as shown in
Part A of Figure II-U. At other locations, it may be better to draw
deep water as shown in Parts B and C of the figure. A complicating
factor is that the desirable water supply depth may vary seasonally or
even diurnally, making multilevel intakes environmentally attractive. A
typical multilevel intake is shown in Part D of the Figure.. For water
sources where the biologic community is extremely sensitive to intake
currents, a deep intake of the infiltration type might be best as shown
in Part E of the figure.
16
-------
^
o
SURFACE INTAKE
(A)
O
<>
•^w^
c
DEEP INTAKE
(3)
DEEP INTAKE
K)
-------
Aguatig Environmental Considerations in Intake Location
The location of the intake should also reflect the knowledge of the
various members of the aquatic community. The location should be
selected to minimize the impact of the intake on the identified species.
In general, the intake location should include the following:
avoidance of important spawning areas, fish immigration paths,
shellfish beds or any location where field investigations have
revealed a particular concentration of aquatic life.
selection of a depth of water where aquatic life is minimum. This
depth may change seasonally or diurnally.
selection of a location with respect to the river or tidal current
where a strong current can assist in carrying aquatic life past the
inlet area or past the,face of screens (if the flush mounted type of
setting is used for example).
selection of a location suited to the proper technical functioning
of the particular screening system to be used. For example, the
still experimental louver and horizontal screen installations have
limiting requirements relative to water level variations and intake
approach channel configurations which will influence their locations
with respect to the source of water.
The application of the above presupposes that sufficient biological
investigation has been conducted to establish sensitive areas and
important species. The previous section of the report outlined the type
of data required in the procedure for biological data gathering. These
data are essential for proper intake location. Furthermore, when
returning bypassed fish and other organisms, they should be delivered to
a hospitable situation.
Intake_Locatign with Respect to the Balance of the Plant
some organisms may undergo damage in the passage from the intake to the
plant and on the return between the condenser and the discharge
structure. The extent of the damage is proportional to the temperature
and pressure changes and the time of travel between the shore and the
plant. Since the time of travel is related to the distance between the
intake and plant, it would be desirable, in cases where incremental
damage due to this effect would be significant, to locate the intake as
close to the plant as possible. This consideration applies even more to
the location of the outfall with respect to the plant. Relocation of an
existing intake with respect to the balance of the plant could be very
costly in many cases.
18
-------
SECTION III
DESIGN
Introduction
This section of the report is organized to describe the various
components which comprise an intake structure. The components described
include screening devices, trash racks and fish handling and bypass
equipment. This organization is utilized to provide an understanding of
the function and configuration of these components. Following this, the
description of components will be assembled into complete descriptions
of intake designs, with recommendations developed for each type of
design. The section is presented in five parts as follows:
Screening Systems Design Considerations
Behavorial Screening Systems
Physical Screening Systems
Fish Handling and Bypass Facilities
Intake Structure Designs
Screening Systems Design Considerations
By far the most important design consideration for screening systems at
intake structures is the velocity through the screens. Intake
velocities are usually measured in two ways as follows:
Approach Velocity - Velocity in the screen channel measured
immediately upstream of the screen face.
Net Screen Velocity - Velocity through the screen itself. This
velocity is always higher than the approach velocity because the net
open area is reduced by the screen mesh, screen support structure
and debris clogging.
Velocity considerations should be based on the approach velocity since
the net screen velocity is constantly changing with debris loading in
the waterway. Another important design consideration is the selection
of the screen mesh size. This should be based on both fish size and
debris loading considerations.
19
-------
Other environmental factors to be considered in designing intake water
screens can also affect the configuration of the intake structure
itself. These factors include proper location of screens to avoid zones
of entrapment, and good hydraulic design to insure uniform flow over the
entire screen face. This latter element is influenced by the design of
the hydraulic passages both upstream and downstream of tne screen. The
downstream design also includes the location of pumps.
Approach Velocities
Most existing water screens at intake structures nave been designed
solely on debris removal considerations. The design criteria is usually
that a relatively low head loss be maintained across the screen at the
lowest water level anticipated. Typical velocities through the screen
mesh fall in the range of 0.61 to 0.762 meters per second (2.0 to 3.0
feet per second) which would correlate to screen approach velocities in
the range of about 0.24 to 0.335 mps. (0.8 to 1.1 fps) or higher.
Hydraulic head loss is an important design consideration since it
controls the pressure loading on all moving parts of the screen. Thus
lowering the head loss across the screen lowers the operating cost of
the screen and increases screen life. Head loss increases as the square
of the approach velocity, and becomes even greater as debris clogging
causes increased turbulance across the screen and reduces the net screen
area. The effect of these factors on head loss is shown in figure III-
1. This plot is based on 0.95 cm (3/8") galvanized wire mesh. Screen
velocity which is related to screen opening is also important because of
its impact on impinged organisms. Physical damage to impinged organisms
will increase in proportion to the velocity through the screens.
Many intermittently operated traveling screens are designed to be
actuated under a maximum lead loss of 1.52 meters (5 ft). Some
traveling screens operate continuously at a lower head loss, generally
0.3 to 6.61 meters (1.0 to 2.0 ft). Some traveling screens are rotated
once every 4 to 8 hours for 5 to 10 minutes for low head losses, rotated
more often for incrementally higher head losses, and run continuously at
high speed for the highest head losses. Many powerplant intakes include
a pump trip-out to shut off the circulating water pumps automatically
when the head loss exceeds 1.52 meters (5 ft) or when the downstream
water level drops to some predetermined level. In the absence of such a
trip-out provision, head differential across the screen will rapidly
increase to the point of screen collapse and possibly damage to the
pumps.
Another important design feature of traveling water screens is the rate
of screen travel when operating. Screens that are not intended for
continuous operation are designed for a single operating speed of 3.05
meters per minute (10 fpm), although speeds as low as 0.61 meters per
minute (2 fpm) and as high as 6.1 meters per minute (20 fpm) have been
used at particular locations. For continuous screen operation (rarely
20
-------
2.14
0
1.83
QC
UJ
fc
Q
2
U.
O
Co
CO
O
0.912
0.60G
0.304
O
0
(FEET/SEC.)
2 3
0.30A 0.606 0.912. 1.22
DESIGN VELOCITY IN METERS/SEC
LOSS OF HEAD THROUGH TRAVELING
WATER SCREENS Q.95 cm(3/8") OPENING
FIGURE III-l
21
-------
used at powerplant intakes) or for use under varying flow conditions,
two speed screens are used, 0.76 and 3.05 mps (2.5 and 10 fps) being the
usual speeds. Screens are generally operated once per shift and are
rotated automatically in response to water level differential across the
screen face. The importance of considering operational frequency and
screen speed characteristics in minimizing impingement effects will be
covered in the subsequent section on operation and mainrenance of intake
structures.
Much of the reported research would indicate that considerably lower
approach velocities than the 0.24 to 0.335 mps (0.8 to 1.1 fps) range
shown above may be required to protect against impingement of certain
species of fish. Table III-1 provides a tabulation of fish swimming
capability of various species taken from Reference 21. The table shows
that fish swimming ability is a function of both fish size and the
ambient water temperature. An inspection of the lower levels of
swimming capability within each species shows that approach velocities
of considerably less than 0.305 mps (1 fps) may be desirable.
Figure III-2 shows the results of additional studies of the impact of
approach velocities on fish impingement. These studies were conducted
at a major nuclear plant in the Northeast and reported in .Reference 8 G.
The involved species were the white perch and striped bass. The figure
shows a marked increase in impingement above intake velocities of
approximately 0.24 mps (0.8 fps). It is important to note that this
study was not done during the critical winter months when fish swimming
ability would be at its lowest.
Figure III-3 shows the results of another study which was reported in
Reference 24. This figure shows the swimming ability of young salmon.
The effects of both size and temperature on swimming ability are
significant. Note, however, that the mean cruising speed for all sizes
is a relatively low 0.15 mps (0.5 fps) for the colder winter
temperatures. Oxygen level, as well as temperature, may be a
determining factor in fish-swimming ability. The selection of the
design approach velocity should conservatively reflect tiie degree to
which the conditions of the laboratory fish-swimming tests correspond to
the conditions of the intake considering that the natural behavior of
the fish and their escape response are based upon a complexity of
factors. Furthermore, it should be recognized that the approach
velocity would influence the ability of fish to avoid the intake screen
if there is not already a horizontal current to move them from the
intake. A further significant parameter could be the current at the
screen itself which would determine the ease of escape of a fish once
impinged and also the extent of damage to the fish while impinged.
22
-------
TABLE III-l
FISH MAXIMUM SWIMMING SPEEDS
NJ
U)
Fish
White Perch
Striped Bass
Stripped Bass
cm
7.9 -
6.1 -
3.0 -
3.3 -
5.1 -
4.1 -
5.1 -
3.0 -
3.0 -
5.1 -
1.9 -
0,25-
Size
8.4
7.1
4.3
4.7
6.8
5.1
6.8
4.8
4.8
6.4
3.8
7.6
7.6 -14.0
King Salmon
3.0 -
3.0 -
3.8
4.8
Range
inch
3.1 -
2.4 -
1.2 -
1.3 -
2.0 -
1.6 -
2.0 -
1.2 -
1.2 -
2.0 -
Q.75-
0.1 -
3.0 -
1.2 -
1.2 -
3.3
2.8
1.7
1.8
2.7
2.0
2.7
1.9
1.9
2.5
1.5
3.0
5.5
1.5
1.9
Water
C
5
10
24
27
27
32
32
24
27
27
_
-
-
_
-
Temp.
F
41
50
75
80
80
90
90
75
80
80
_
-
-
_
-
Maximum Speed
all - best all - best
mps fps
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.16 -
.19 -
.12 -
.15 -
.22 -
.22 -
.28 -
.18 -
.18 -
.33 -
.28 -
.55 -
.49 -
.28 -
.15 -
0.25
0.23
0.30
0.30
0.40
0.40
0.43
0.33
0.40
0.43
0.43
0.88
0.88
0.52
0.46
0.52
0.63
0.4
0.5
0.7
0.7
0.9
0.6
0.6
1.1
0.9
1.8
1.6
0.9
0.5
-0.81
- 0.77
- 1.0
- 1.0
- 1.3
- 1.1
- 1.4
- 1.1
- 1.3
- 1.4
- 1.4
- 2.9
- 2.9
- 1.7
- 1.5
-------
80
(FEET/SEC.)
0.6 0,8
1.0
1.2
1.4
60
or
O-
40
ID
o
f,;
U.
20
RESULTS OF DATA OBTAINED SPRING, 1966
CURVE RESULTING FRCH DATA OBTAINED FALL, 1965
0
0.0
0.061 0.122 0.183 0.244 0.305 0.366
AVE3ASE INTAKE CURRENT VELOCITY IN METERS/SEC.
INTAKE VELOCITY VS FISH COUNT
FIGURE III-2
0.426
UJ
c/)
•o
30
UJ
Q_
MEAN SLOPE
COHO UNDER YEARLINGS CONO YEARLINGS
1.5
1.0
Lu
0
23456789
MEAN FORK LENGTH, CM.
10
0
MEAN CRUISING SPEED FOR UNDER YEARLINGS AND
YEARLING COHO SALMON FOR FOUR LEVEL OF ACCLIMATION
FIGURE III-3
24
-------
Effective Screen Length and Uniform Velocities
It is important to determine the effective dimension of screen below the
water line to be used in calculating the approach velocity. Not all of
the screen length below the water line contributes effectively to
screening. The effective length of screen is influenced by both the
hydraulic design of the intake and by bottom effects related to the
screen boot, boot plate, etc. Another important consideration in deter-
mining the effective screen length is the effect: of upstream
protrusions, particularly the effect of curtain walls installed to
select intake waters from the top or bottom layers of the water body.
The effect of walls on the effective screen area is snown in Figure
III-4. The illustration shows a wall installed to limit araft to the
lower levels of the water body. The wall limits the flow through the
screen area to a relatively narrow band at the bottom of the screen as
indicated on the figure. If walls are installed, only the effective
screen area should be used to determine the approach velocity. Walls
can also be undesirable when they create dead spaces where fish can
accumulate and from which they may not be able to escape.
Another important design consideration is the uniformity of velocities
across the full face of the screen. An example of poor hydraulic design
is shown in Figure III-5. The sketch shows large variations in channel
velocities which greatly reduce the effectiveness of the screen. To
eliminate these undesirable conditions, the relative locations of pumps,
screens and any upstream protrusions should be carefully studied. The
standards of the Hydraulic Institute recommend screen to pump distances.
However, these are based on pump performance criteria only. Any radical
departure from standard intake design should be modeled to establish the
actual screen velocity and the extent of any localized variations.
Selection of screen Mesh Size
The selection of screen mesh size is generally based on removal of trash
that could clog condenser tubes. A generally accepted rule of thumb for
selecting the screen mesh size is that the clear openings in the screen
should be limited to about half the diameter of the heat exchanger
tubes. The powerplant industry has become fairly standardized on a 0.95
cm (3/8") mesh size (equivalent to 1.9 cm (3/4") ID tubes) even though
longer condenser tubes are used in many condenser designs.
The effect of screen mesh size on the performance of screens is quite
significant as shown in Table III-2. The data were supplied by a
leading screen manufacturer. The table shows that the screen
efficiencies (ratio of net open areas of the screen to total channel
area) decrease rapidly as the mesh size decreases. The table also shows
that using alloy metals in place of galvanized metals will increase the
screen efficiency as will the use of wider and deeper screens. Alloy
metals are generally used to inhibit corrosion in high salinity waters,
such as experienced in ocean cr estuarine intakes, or in other corrosive
waters. PVC screen mesh is also used. The effective area is less than
25
-------
TRAVELING
CURTAIN WALL-x RSH
SUCTION PUMP
OF
SCREEN
ACTUALLY
EFFECTIVE
EFFECTIVE SCREEN AREA
FIGURE III-4
26
-------
NOTES:
I. VELOCITIES SHOWN IN METERS/SET.
2 MEASUREMENT MADE BETWEEN DEICING LOOP PIPE AND BAR RACKS
(Kl MARCH 1970.
a MEASUREMENT MADE DURING THROTTLED CIRCULATING WATER FLOW,
AT 30% OPEN.
UNDESIRABLE INTAKE WELL VELOCITY PROFILES
FIGURE III-5
27
-------
TABLE II1-2
NJ
CO
TRAVELING WATER SCREEN
EFFECIENCIES
Clear
Opening
cm.
0.32
0.48
0.63
0.95
1.28
1.58
Size
in.
1/8
3/16
1/4
3/8
1/2
5/8
Wire
Material
Alloy
Galv.
Alloy
Galv.
Alloy
Galv.
Alloy
Galv.
Alloy
Galv.
Alloy
Galv.
Selection
Diameter
cm.
0.12
0.16
0.12
0.16
0.12
0.20
0.20
0.27
0.27
0.34
0.27
0.34
in.
.047
.063
.047
.063
.063
.080
.080
.105
.105
.135
.105
.135
W&M
Ga.
18
16
18
16
16
14
14
12
12
10
12
10
0.61
(2)
.322
.334
.511
.445
.510
.459
.543
.488
.546
.496
.587
.541
0.91
(3)
.431
.361
.522
.457
.451
.469
.555
.498
.558
.506
.600
.552
1.22
(4)
.436
.365
.527
.462
.526
.474
.560
.503
.566
.512
.606
.558
Screen
1.52
(5)
.438
.367
.530
.465
.530
.476
.564
.506
.567
.515
.609
.561
1.82
(6)
.440
.368
.533
.467
.532
.478
.566
.508
.569
.517
.612
.563
Basket
2.13
(7)
.441
.369
.534
.468
.533
.479
.567
.509
.570
.518
.613
.565
Width Meter (Ft)
2.44
(8)
.442
.370
.534
.468
.534
.480
.568
.510
.571
.518
.614
.565
2.74
(9)
.442
.370
.525
.469
.535
.481
.569
.511
.572
.519
.615
.566
3.05
(10)
.443
.371
.536
.470
.535
.482
.570
.512
.573
.520
.616
.567
3.35
(11)
.444
.371
.537
.471
.536
.483
.571
.513
.574
.521
.617
.568
»
3.64
(12)
.444
.372
.537
.471
.536
.483
.571
.513
.575
.521
.618
.568
3.96
(13)
.445
.372
.538
.472
.537
.484
.572
.514
.575
.522
.618
.569
4.26
(14)
.445
.373
.539
.473
.538
.485
.573
.515
.576
.523
.619
.570
Alloy wire: Copper, stainless, monel, etc. - greater corrosion resistance permits use
of smaller diameter wire, improves efficiencies.
-------
for wire mesh for a given screen size. Thus if mesh velocity is a
limiting criteria (rather than screen approach velocity) the total
screen area must be greater.
Some work has been done toward establishing screen mesn size as a
function of the size of fish to te screened. Reference 24 reports the
following empirically derived relationships:
M = O.OU (L-1.35)F; 5
-------
0.0
7.5
£
-------
these reasons, most behavioral systems have not demonstrated consistent
high level performance.
In addition, all behavioral systems require a passageway to allow the
fish to move away from the stimulus. The location and configuration of
the required passageway is often more difficult to develop than the
behavioral barrier itself. The following discussion traces the
development of several of the behavioral screens in an attempt to
establish their applicability in intake design.
Electric Screens
The basis of the electric screen approach is described in Reference 18
and is shown in Figure III-7. Immersed electrodes and a ground wire are
used to set up an electric field which repels fish swimming into it.
The important design parameters in electric screening are the spacing of
electrodes, the separation between rows of electrodes, the voltage
applied to the system, the pulse frequency, the pulse duration, and the
electrical conductivity of the water. Typical design parameters for
both test systems and full-scale systems are shown in Table III-3. The
data for this table were taken from Reference 13. Most of the test
systems established by the former U. S. Fish and Wildlife Service (now
the U. S. Bureau of Sportfish and Wildlife) were applied to repel (and
divert) upstream migrating fish (adult fish). In most waters, but
particularly in brine or salt waters, conductivity can vary widely with
stream flows, tidal changes and storms, thus creating a need for proper
adjustment of the electric screens to maintain the electric potentials
desired.
Typically, salmon respond to the screen in the following manner. They
swim upstream against the flow, enter the electric field and jump
violently back away from it, retreating several hundred feet downstream.
After several attempts and shocks they approach more slowly and follow
the angled electric field to the safe passageway provided. If they are
immediately stunned, the downstream current will carry them safely away
from the screen.
The electric screen has the advantage of flexibility and may r>e applied
intermittently during time of need for intake protection. The major
disadvantages of the electric screening system are as follows:
Cannot be used to screen downstream migrants.
Cannot be used to screen a mixture of sizes and species because
of different reactions that are size and species related.
Cannot be used in esturarine or ocean waters because of high
electrial losses.
31
-------
LIN6 OU S|Et AM «.OT JOM
A
PLAN
O.'C.
ELEV. A-A
TYPICAL ELECTRIC FISH FENCE
FIGURE. III-7
32
-------
TABLE III-3
ELECTRIC SCREEN APPLICATIONS
SUMMARY OF DESIGN DATA
Location
*Pacif ic
Northwest
*Pacif ic
Northwest
*Pacif ic
Northwest
*Idaho
San Diego
(water intake)
Indiana (Power-
plant #1809}
N. Y. (Power-
plant #3608)
Specie
Squawf ish
Salmon
f ingerlings
Salmon
f ingerlings
Squawfish
Mixed
Perch
Fresh water
game fish
Barrier
Description
2 rows 0.46m (18") apart
5.0cm (2") 0 electrodes
in parallel rows @ 40°
angle to flow
5.0cm (2") 0 tubular
aluminum electrodes
@ 0.51m (20") spacing
in parallel rows
NA
NA
2 parallel rows 0.45m
(18") apart 0.30m (12")
spacing between electrodes
3.2cm (IV) <£ electrodes
@0.3m (12") spacing in
rows spaced 0.91m (3')
apart
Source
Voltage
(Volts)
60
NA
210
140
500-900
300-600
120
Pulse
Frequency
(Pulses/sec)
2
8
3-4
10
2-3
1-5
Continuous
Pulse
Duration
(Milli/sec)
10-30
40
20-40
50
10
NA
Continuous
Performance
good
68% diverted
82% diverted
80% diverted
effective for
large fish
effective
effective
Test systems
-------
Can be dangerous to both humans and animals because o± the high
voltages used.
The Fish and Wildlife Service terminated its research on electric
screens in 1965. Over fifteen years of concentrated research had failed
to solve many of the major problems of electric screening systems.
Several utilities have investigated the problem in depth and some
research is still being conducted,but not much success has been shown to
date for downstream-migrant fish. In summary, electric screens, while
not generally successful, may work in some situations.
Air Bubble Screens
The fish response employed by an air bubble screen is avoidance of a
physical barrier. In its simplest form, the bubble barrier consists of
an air header with equally spaced jets arranged to provide a continuous
curtain of air bubbles over the entire stream cross section, as shown on
Figure III-8.
Historically it was also felt that the sensory mechanism involved in
utilizing the air bubble screen was entirely visual. This led to the
conclusion, long held, that the screen was not useful at night. More
recent findings of experiments conducted by a leading manufacturer.
Reference 30, tend to refute this belief. Design and performance data
at two existing power stations are also presented. In one case the
screen was successful and in the other unsuccessful.
The laboratory tests referred to were conducted at the Edenton National
Fish Hatchery in North Carolina. The experiments were conducted with
striped bass and shad, 80mm to 250mm in length.
The test channel used is shown in Figure III-9. The results of the
tests are reported in Reference 30 and are summarized as follows.
When the air bubble curtain was placed entirely across the 1.2m (4')
channel, the fish would not pass through in any of the tests, even
when attempts were made to chase them through the curtain.
Temperature does influence the performance of the barrier. The
tests were conducted at 10°C, <4.5°C and 0.8°C (50°F, 40°F, and
33.5°F). The bubble barrier was a complete success at 10°C(50°F)
and at 4.5°C(UO°F). At 0.8°C(33.5°F) the fish were lethargic and
simply drifted through the barrier with the current. This
limitation would be shared with all systems which rely on swimming
ability of fish to escape an intake.
This particular bubble barrier appeared to be as successful in
complete darkness as well as in daylight. This tends to refute the
34
-------
AIR BUBBLE SCREEN
TO DIVERT FISH FROM WATER INTAKE
FIGURE iii-8
35
-------
vet.
PLASTK
TAUWL
\ 1
" \
feofc&U
PLACED
1.0 -
0,3-
S6CTIOU
J
^ FLovs/
)
>.2yi
(41)
TTP.
— PUMPS
PLAN
0.29M TO
CU" TO t&") DEPTH
Op
CHANNEL TO TEST EFFECTIVENESS OF AIR BUBBLE SCREEN
AT NORTH CAROLINA FISH HATCHERY
FIGURE III-9
36
-------
long held conclusion that these systems will not work at night. It
also indicates that sensory mechanisms other than visual are
involved, and that future work is required to define fish response
to this type of situation.
The air was injected through 0.08 cm (1/32") round holes at 2.5 cm
(1") spacing. At 5.0 cm (2") tc 7.5 cm (3") spacing tne fish would
pass between the rising bubble columns.
When the bubble system was placed 5.0 cm (2") off the floor, fish
would not pass under it. When placed any further off the floor of
the channel, the fish would pass unimpeded under the curtain.
A successful application of an air bubble screen was reported in
Reference 13. The system was installed at a powerplant intake (plant
no. 5521) on Lake Michigan in Wisconsin. The principal fish species
involved was the Alewife, a variety of herring which is a neavily
schooling fish having a length between 15 and 20 cm (6" and 8"). The
plant has an average cooling water flow of some 18.3 m3/sec (290,000
gpm). The air bubble barrier extends across the intake channel, well in
front of the intake structure in about 3.6 to 4.0m (12' - 13') of water.
The air bubble system consists of 2.5 cm (1") diameter PVC lines with
holes drilled on 10 cm (4") centers. The total air flow is
approximately 0.047 m3/sec (100 cfm) at 413.7 Ktt/m2 (60 psi). The air
is supplied by a conventional compressor drawing 15,000 to 19,000 W (20
- 25 hp) . The optimum air flew was measured at 0.01 m3/nun (0.36 cfm)
per 0.3 m (1 foot) of air header at 413.70 KN/m2 (60 psi).
Prior to the installation of the air bubble screen, there had been
several shutdowns of the plant caused by schools of Alewives jamming the
screens and shutting off the flow of cooling water. Since the
installation of the screen, there has been only one or two shutdowns of
this type during more than four years of operation. The major purpose
of the air bubble screen is tc repel schools of fish rather than to stop
all individuals. The operation cf the bubble system at this plant has
been equally successful at night as in daylight. The operation of this
system was considered so successful that another utility located on Lake
Michigan is installing a similar system at a new nuclear station.
(plant no. 5519)
The performance of a similar system installed at a major nuclear station
in the Northeast (plant no. 3608) was exactly opposite of that described
above. The species involved at this plant were the striped bass and
white perch. When the plant first went on line, there was a serious
loss of larger fish on the screens. A series of modifications were made
in an attempt to reduce the loss. The modifications are shown in Figure
111-10 and consisted of the following:
Removal of eight feet of the original curtain wall to reduce the
intake velocity. Average velocity over the face of the screen
37
-------
c.w. PUMP
BUBBLE SCREEN INSTALLATION AT PLANT NO. 3608
TO REPEL FISH FROM WATER INTAKE
FIGURE 111-10
38
-------
before the modification was about 0.30 m/s (1 fps). After making
the change, the summer average velocity was 0.18 m/sec (0.60 fps),
and the winter average velocity was 0.048 m/sec (0.15 fps) .
The installation of a fixed screen mounted flush with the front face
of the intake to allow the fish to swim to the right or left to
escape entrapment. This modificaticn also eliminated the entrapment
zone between the face of the screen and the existing vertical
traveling screen.
The installation of an air bubble system in front o± one of the four
bays of the intake. The bubble system consisted of two vertical
rows of horizontal bubbler pipes. The first row was located three
feet in front of the intake and the second row was located six feet
in front of the intake. Each row of bubbler pipes has seven
horizontal pipes in a four foot center to center spacing. Air was
discharged through 0.08 cm (1/32 inch) opening at 1.3 cm (0.5 inch)
center to center spacing. The first tests were run with 0.424 m3/s
(900 cfm) of air which was far too large a quantity. The surface of
the water in front of the intake rose by as much as one foot in
violent churning action. The entrained air caused vibration
problems in the pumps. The quantity of air was subsequently reduced
to 0.189 m3/s (400 cfm) which is the design value used in modifying
all bays. The total cost fcr modifying both intakes at this plant
in the manner described was approximately $1,000,000.
The results of these modifications are as follows:
The intakes now impinge fish of a smaller size (50 to 100 nun) rather
than the larger sizes that were entrapped before the modification.
The effect of the air apparently was to reduce the number of fish
entering the bay equipped with the bubble system, but the number of
fish entering the remaining three bays increased.
During July 1972 tests, the test engineers were able to discern no
improvements in fish entrapment during the daytime; at night the
fish being trapped in the bay equipped with the bubble system
appeared to be significantly greater than in the bays with no
bubbler.
The bubble barrier did appear to be effective in controlling ice in
front of the intake during freezing conditions. This fact makes the
bubble system attractive as a possible replacement for the hot water
recirculation systems which are currently being used to control ice
at many existing installations. The problems associated with hot
wa^er recirculation have been discussed in an earlier section.
In summary, the air bubble system may have some application at certain
types of intakes. The system appears to be most effective in repelling
39
-------
schooling fish. However, tne mechanism of bubble screening is not
sufficiently well understood to recommend its adoption generally.
Behavioral Systems Employing Changes in Flow Direction
The propensity of most species of fish to avoid abrupt changes in flow
direction and velocity has been demonstrated on several occasions. This
ability of fish to avoid horizontal change in direction and velocity is
the principle on which the louver fish diverting system is based. On
the other hand, fish are generally insensitive to changes in vertical
flow characteristics. This indifference of most species to vertical
changes in flow regimen is the principle upon which the "fish cap"
intake is based.
Louver Barrier
The principle of the louver diverter is illustrated in Figure III-ll.
The individual louver panels are placed at an angle o± 90° to the
direction of flow and are followed by flow straighteners. The abrupt
change in velocity and direction form a barrier through which the fish
will not willingly pass if an escape route is provided. The stream
velocity is shown in the figure as Vs. Upon sensing the barrier the
fish will orient himself perpendicular to the barrier and attempt to
swim away at a velocity Vf. The resultant velocity VR carries the fish
downstream roughly parallel to the barrier to the bypass located at the
downstream end of the barrier. The controlling parameters in the design
of the louver system are the channel velocity VS, the angle of
inclination cf the barrier with respect to the channel flow (10° to 15°
recommended) and the spacing between louver panels which is related to
the fish size.
Most of the current performance data on the louver design have come from
tests of two prototype installations at an irrigation intake operated by
the California Department of Fish and Game in the Sacramento-San Joachim
delta of California. 2* The Delta intake is shown on Figure 111-12.
The facility is designed for a flow of 170 in3/s (6,000 cfs) , and was
tested at approach velocities tc the louver of 0.46 to 1.08 m/s (1.5
3.5 fps) with bypass velocities of 1.2 to 1.6 times the approach
velocity.
The efficiency of the louver system drops severely with increase in
velocity through the louvers. For velocities of 0.46 to 0.61 m/s (1.5 -
2 fps), efficiency was 61% with 15 mm fish and 95* witn 40 mm fish.
When the velocity was increased to 1.08 m/s (3.5 fps), efficiency was
35% for 15 mm (0.6 in) fish and 70% for 40 mm (1.6 in) fish. The
following conclusions were reached as a result of these tests.
Efficiency increases markedly with fish size.
40
-------
ClEAB. SPACE- BfcTweCU
F]5V4 BYPASS
LOUVER DIVERTER-SCHEMATIC
111-11
-------
DELTA FISH FACILITY PRIMARY CHANNEL SYSTEM
FIGURE 111-12
-------
Efficiency increases with lower channel velocities.
Addition of a center wall improves the efficiency, giving the fish a
wall to swim along if he wishes.
Very careful design is required to take account of the many
variables, such as bypass ratios, guide walls, approach velocity,
louver angle, etc. Each application would most likely require
extensive model testing to define optimum design parameters, for the
species of concern at the temperature anticipated for each size to
be dealt with.
Individual louver misalignment did not have much effect. In fact,
efficiency even improved with a deviation from the exact alignment.
Swimming capacity is length related.
The major disadvantages of the fixed louver system are the following:
The shallow angle of louvers with respect to the channel flow
requires a rather long line of louvers which will increase the cost
of the intake.
The louver system does not remove trash. A second set of
conventional screens are required downstream of the louvers for
trash removal. The performance of the louver may be adversely
affected in streams with a heavy trash load.
A rather complex fish handling system is required to safely return
fish to the water source.
Water level changes and flow variations must be kept small to permit
maintenance of the required flow velocity.
In an attempt to overcome some of these limitations, additional studies
were conducted at a major power station in Southern California (plant
no. 0618). Of the major fish types studied, the anchovy of about 130 mm
(5.2 in) in length was the most delicate. Another sensitive fisn (200
mm (8.0 in) in length) was the queen fish. The strongest and toughest
fish included white perch and croakers. A sketch of the test flume is
shown in Figure 111-13 and results reported in Reference 32 were as
follows:
The louver efficiency increased with flow up to 0.61 m/s (2 fps)
which was considered optimum.
The bypass design is very important. The optimum Bypass velocity
was determined to be 1.08 m/s (3.5 fps), a ratio of 1:1.5 with
channel velocity.
43
-------
T .
AUGtt WAS
VAC. 16t>.
20°
* TO ?i(
PAUEL- ALSO KAU
MESH
PLAN
TEST FLUME AT PLANT NO. 0618
FIGURE III-13
44
-------
A 2.5 cm (1") louver spacing gave good results. Increasing the
louver spacing to 4.5 cm (1.75") reduced efficiency significantly.
The louvers should have a 20° or less angle with flow direction.
Increasing this angle markedly reduced louver efficiency.
The louver system worked as well at night as during the daytime.
The experience gained in these tests is being used to design a new
intake for a major nuclear installation (plant no. 0629). A sketch of
this intake is shown in Figure 111-14.
The intake employs the louver principle described above. The louvers
are mounted on frames similar to the conventional water screens.
Instead of the fixed louver system, the louvers are rotated in a manner
similar to a traveling bar screen used in municipal wastewater
treatment. A water jet system washes any material from the louvers as
it passes over a standard trash trough. Behind these vertically
traveling louvers is a standard vertical traveling fine screen similar
to that used at most powerplant intakes. The louvered frames are so
mounted that the front of the frame is flush with the walls supporting
the entire mechanism so that fish may move unimpeded down the face of
the louver vanes. The louver vanes serve as trash racks.
A very important element of the intake is the guide vane system upstream
of the louver faces. These vanes insure that the flow does not turn
before it reaches the louver.
Fish moving down the face of the Icuvers enter a bypass. The bypass
itself has a unique fish lifting system, Figure 111-15, which litts the
fish up several feet, where they can be dropped into a channel lor their
return to the sea. Supplementary water is also pumped into this
channel.
A very substantial amount of model testing was required to develop this
intake. The model work included the test flume, the test set up for the
lifting basket and all its flow mechanisms, the detailed intake
structure itself and the detailed bypass system.
While it will be several years before performance data on tins intake
will be available, its successful operation would represent a large step
forward in intake design. The louver principle has been demonstrated
both in model and in large prototypes and should have a significant
impact on future design of intakes. The cost of installing tins type of
intake will be substantially higher than those of a conventional intake.
45
-------
COUVEUTlOUAL
"BAR
B.W6C.
K. V
X
P L
INTAKE STRUCTURE - PLANT NO. 0629,
TO DIVERT FISH BY LOUVER SCREENS AND RETURN THEM DOWNSTREAM
FIGURE HI-14
4.6
-------
i
"
VJ
A
I5CM
2.1M
SI
PLAN
to
3
0
seen
BASKET
SECTION
FISH ELEVATOR FOR FISH BYPASS - PLANT NO. 0629
FIGURE 111-15
47
-------
"Velocity Cap" Intakes
The operation of a velocity cap is shown in Figure 111-16. It is based
on laboratory studies which shew that fish do not respond to vertical
changes in direction, whereas they show a marked ability to avoid
horizontal changes in velocity. By placing a cover over the top of a
intake, the flow*'pattern entering the pipe is changed from vertical to
horizontal. As shown in the illustration, the cap has a rim around its
edge to prevent water sweeping arcund the edge and to provide more
complete horizontal flow at the entrance.
a
Velocity caps have been used since 1958, when one was installed at
ocean-sited power station in California (plant no. 0623). Several other
plants in southern California have adopted the concept since then. One
problem with the utilization of the velocity cap is that it is difficult
to inspect, since it is under water. Frequently, the only sign that the
cap is not working properly is an increase in fish on the screens.
Other Behavioral Systems
Other behavioral mechanisms have been experimented with in conjunction
with fish diversion. These include sound barriers, light barriers and
several types of fish attraction systems. The types of experiments
conducted in regard to these systems have generally been more cruae than
those discussed earlier. Consequently, the results are generally less
conclusive indicating that considerably more formal investigation is
required before these sytems can be fully evaluated.
Light Barriers
The same test flume shown in Figure 111-13 and discussed in Reference 30
was also used to test a light barrier system. Upon approaching a
1-iqtr- barrier placed across the full width of the flume for the first
tim«" during the rest, the fish would mill around for 3 to 5 minutes
befor- passing through. On subsequent trips around the flume, they
would hesitate less and less until the time for each circuit was reduced
^c that which existed without the light source. This indicates that the
fish rapidly become acclimated to light which renders such a barrier
us-less. O^her experiments with the same apparatus using light in
conjunction with a bubble curtain were also unsuccessful. It was con-
cluded from these test that light had no effect from a practical
s^-ancipo^r.-*-. As far as could be determined, there are no existing
ir^a'kf-s~wh~re a xight barrier is functioning successfully. Light also
has -h^ adverse effect of attracting fish under certain circumstances
and has resulted in the complete shutdown of plants.
Souia Farriers
Fish have been shown to respond to sound of high intensities and low
frequencies, but become accustomed to constant sound levels. It has
48
-------
VD
Velocity Distribution Without Cap
Velocity Distribution With Cap
OPERATION OF THE VELOCITY CAP
FIGURE 111-16
-------
been shown that minnows respond to frequencies up to 6,000 Hz and
catfish to 13,000 Hz or only slightly less than the 15,000 Hg band
considered normal for humans. Cther fish respond to frequencies up to
only 1000-2000 Hz and are less sensitive to sound intensity. This high
variability to sound among different species is a major drawback to this
type of system.
There have been many attempts to direct fish around intake structures
using sound barriers. A recent installation at a major nuclear station
in Virginia (plant no. 5111) employed reck and roll music broadcast at
relatively high intensities under water. This type of music was
selected because of its multi-frequency nature and because it is non-
repetitive. The conclusion was that the system appeared to be at least
partially effective. However, due to the many species and and sizes
involved and the diversity of responses, it was decided to install a
mechanical system to reduce the fish entrapment problem. The sound
system will continue in use while the mechanical system is being
installed. A discussion of the proposed mechanical system is contained
in another section of this report.
Applicability of Behavioral Screening System
In summary, none of the behavioral systems have demonstrated
consistently high efficiencies in diverting fish away from intake
structures. The systems based on velocity change appear to be
adequately demonstrated for particular locations and species, at least
on an experimental basis. More data on the performance of large
prototype systems at powerplants will te required before the louver
system can be recommended for a broad class of intakes. The velocity
cap intake might be considered for offshore vertical intakes since it
would add relatively little to the cost of the intake and has been shown
to be generally effective in reducing fish intake to these systems.
The performance of the electric screening systems and tne air bubble
curtains appear to be quite erratic, and the mechanisms governing their
application are not fully understood at the present. These types of
systems might be experimented with in an attempt to solve localized
problems at existing intakes, since the costs involved in installing
these systems is 'relatively small.
No successful application of light or sound barriers has been
identified. It appears that fish become accustomed to these stimuli,
thus making these barriers the least practical of the available
behavioral systems on the basis of current technology.
50
-------
Physical Screening Systems
All cooling water intake systems employ a physical screening facility to
remove debris that could potentially clog the condenser tubes. Such
facilities range from simple stationary water screens to filter beds.
This sub-section will consider only mechanical screening mechanisms. In
general, these mechanical screens have been developed to protect the
powerplant from debris, rather than to protect aquatic life.
In other sections intake facilities are reviewed as a whole, with
further consideration of the installation and operation cf some of the
mechanical systems discussed here. Also reviewed in other sections is
the important area of fish repulsion systems based on the oenavioral
characteristics of fish.
The following mechanical screening devices are the principal types which
are either in common use or have been suggested for use in powerplant
circulating water systems, both in the United States and abroad.
1. Conventional vertical traveling screens
2. Inclined traveling screens
3. Fixed screens
4. Perforated pipe screens
5. Double entry, single exit vertical traveling screens
6. Single entry, double exit vertical traveling screens
7. Horizontal traveling screens
8. Revolving drum screens - vertical axis
9. Revolving drum screens - horizontal axis
10. Rotating disc screens
Most of the types of revolving drum and rotating disc screens are
commonly used in powerplants outside the United States and have been
supplied by European manufacturers. They have not been used in the
United States, with the exception of a few experimental screens which
will be discussed.
Conventional Vertical Traveling Screens
By far the most common mechanically operated screen used in U. S.
powerplant intakes is the vertically rotating single entry band type
51
-------
screen mounted facing the waterway. A catalogue cut of this screen is
shown in Figure 111-17. Figure 111-18 is a schematic drawing showing
the principal operating features.
The screen mechanism consists of the screen, the drive mechanism and the
spray cleaning system which requires a means for disposal of the waste
materials removed from the screen. The screen is attached to an endless
chain belt which revolves in the vertical plane between two sprockets.
The screen mesh is usually supplied in individual removable panels
referred to as "baskets" or "trays". A continuous band screen is also
available but is not often used. The entire assembly is supported by
two or four vertical steel posts. Longer and wider screens usually
require the stronger four post box structure for support.
The screen washing system consists of a line of spray nozzles operating
at a relatively high pressure 550 to 827 KM/m* (80 - 120 psi). The
washing system may be located at the front or the rear of the screen, or
both. The usual location is in front as shown in Figure 111-18. The
quantity of water required for spray cleaning is in the order of 0.372
m/s (98.42 gpm) per meter (3.28') of screen width. It is supplied
either by booster pumps taking suction from the circulating water pump
discharge or by separate vertical shaft pumps. The disposal of the
debris is usually accomplished by discharging the screen wash waters
from individual screens to a common disposal trough located at the floor
on which the screen is mounted. The trough drains eitner to a debris
storage compartment or directly back to the waterway. If a debris
storage compartment is used, the water is allowed to drain from the
bottom of the compartment and the remaining refuse is periodically
removed to a land disposal area. Both the drive shaft and the screen
wash system are enclosed in a removable housing to protect the drive
components and to contain the high pressure water spray.
The conventional vertical traveling screen has several advantages. It
is a proven off-the shelf item and is readily available. It performs
efficiently over a long service life and requires relatively little
operational and maintenance attention. It is applicable to almost all
water screening situations. It is available in lengths up to about 30
meters (1001) and 15 cm (6") increment widths up to 4.26 meters (14').
The system adapts easily to changing water levels. The screen is
relatively easy to install. Major components of the system, including
supports, baskets, drive mechanisms, and spray systems are standardized.
Special materials for corrosion protection and greater durability are
also available.
The system as presently used has several undesirable features that can
cause adverse environment impact. The most important of these is the
fact that any fish impinged on the mesh of the screen will probably be
destroyed. This effect results from both the design of the system and
the way it is operated. Most traveling water screens are operated
intermittently, not continuously, and fish are pinned against the screen
52
-------
Head
terminal
Electrofluid
Motogear
Spray pipes
and nozzles
Head
sprocket
Foot shaft
CONVENTIONAL VERTICAL TRAVELING SCREEN
Figure 111-17
53
-------
opee-AyiUG oecK
^
CONVENTIONAL VERTICAL TRAVELING SCREEN
FIGURE 111-18
54
-------
for extended periods of time. When the screens are rotated the fish are
removed from the water and then subjected to a high pressure spray, both
of which may be lethal. Any fish surviving these hazards will be
destroyed in the subsequent refuse disposal operations, if the refuse is
not returned to the waterway.
The above discussion suggests the following possible avenues for
correcting some of the environmental defects of the conventional
traveling water screen:
a. reduce impingement time by continuous operation of the screen.
b. provide a path for rapid and safe return of fish to the
waterway.
c. mount the screen so as to provide fish escape passages to either
side, a feature discussed in the section concerning overall intake
design.
The current design of traveling water screens and the screen structures
themselves would not require radical changes to adopt the first two
corrective measures. Several intake designers and screen manufacturers
have proposed modifications of this type in past years and at least one
major nuclear station (plant no. 5111) is modifying its screen baskets
and operational procedures to provide fish protection. These
modifications are discussed in a subsequent portion of this report.
Inclined Screens
Two basic types of inclined screens are available. The first, shown in
Figure 111-19, is merely an adaptation of the conventional vertical
traveling screen. It is used at installations where the debris loading
is extremely heavy and is of a nature that does not readily adhere to
the screen. The downstream inclination of the screen (usually 10° to
vertical) allows debris falling off the lip of one basket to be caught
in the following basket rather than falling back into the waterway.
Also, by inclining the entire screen frame, debris being lifted from the
channel is supported more fully by the ascending basket lips and the
backward tilted screen wire. This type of screen thus might be
advantageous in insuring more rapid removal of fish, shellfish and
jellyfish from the waterway for subsequent bypass as discussed above.
The number of installations using this screen is relatively small and
the system has the same advantages and disadvantages as the vertical
traveling screen. The cost of this screen would be slightly higher than
that of the vertical screen, due to the longer screen well required, the
use of two rows of spray nozzles and other minor variations from the
conventional vertical screen.
The second type of inclined screen has been designed specifically with
fish protection in mind and has significantly different design features
55
-------
tn
TRAVELING WATER SCREEN
FIGURE 111-19
1
!i
vO|
u>u-
DO"
•secyiouA-A
-------
than the conventional vertical traveling water screen. This type of
system is shown in Figure 111-20.
It is still in the experimental stage, but such a screen has been used
successfully in Canada to divert downstream migrating fish and its
performance is reported in Reference 21. This system employs a fixed
screen inclined downstream at an extreme angle to the vertical. The
rear portion of the screen is bent horizontally over the fish collection
trough. The screen is cleaned by a continuous chain flight conveyor
similar to that used in conventional water and wastewater sedimentation
practice. The differences are the orientation of the collector above
the screen and the conveyor flights which are made of a pliable brush
material rather than solid metal. By orienting the screen and cleaning
mechanism in this manner the fish can be slowly herded up the screen and
kept immersed in water until it is dumped gently into me bypass trough.
This design avoids many of the pitfalls of impingement on vertical
traveling screens. The fish is not really impinged in the real sense of
the word. He never leaves his normal habitat of water and is not
subjected to the extreme pressures of the conventional system spray
wat er.
The system has some important limitations. It is very sensitive to
fluctuations in water level, since the water level variation at the
horizontal section of screen must be limited to a few inches; a level
control mechanism such as the slide gate shown in Figure 111-20 is thus
required. Another disadvantage is that the cost of the intake structure
for this type of screen would be significantly increased. The shallow
angle of placement with respect to the incoming flow causes the length
of the intake channel to be several times longer than that required for
the vertical traveling screen of the same screening capacity.
The application of this type of system, as well as several others to be
discussed, is limited in many areas because of the regulations of
cognizant water quality control agencies. Reference here is to the
common policy which prohibits the subsequent discharge of any debris
after it has once been removed from the waterway.
As can be seen from Figure III-20, the method of diverting fish to the
bypass trough also allows for the discharge of the debris back to the
receiving water. Prohibition of this debris discharge would also result
in the prohibition of safe fish return. it is apparent that the same
comment applies to the discharge from the conventional traveling screen
previously discussed. However, in certain cases fish can be separated
from the debris.
Fixed Screens
This term is applied to a number of different types of screens, some of
which are permanently anchored below the waterline of intake structures
57
-------
30
,
SHOTT€|LHO»ST
Q*&&ys2~::.r.-.-'.'
.1 ..^-...-x -r.! > < ?
•.-."•.•---•-:•- - • -
AMD
INCLINED PLANE SCREEN WITH FISH PROTECTION
FIGURE IH-20
-------
and others, the more common, which can be moved but are not capable of
continuous travel. Taken together "fixed" screens, (or "stationary"
screens), constitute the second largest group of physical screening
devices presently found in powerplant intakes. Examples of two types of
screening systems in this category are shown in Figure C-II1-21. Note
that both types of screen would not be used at the same intake and are
only shown on the same figure for convenience.
The first type of screen is mounted upstream of the pumps in vertical
guides to allow them to be removed to a position above the water line.
Figure III-21 shows a relatively sophisticated installation wherein two
rows of screens are provided to permit one to remain in service while
the other is being changed. in addition, each row is divided into two
sections in a manner which allows removal of the lower section without
removal of the upper section. Some debris and fish can be sucked into
the pump during the process of changing screens. The screen guides are
sometimes extended above the deck to hold the raised screens in place
for cleaning. Figure III-22 is a sketch showing typical fabrication
details of such a screen.
Another fixed screen type involves attaching a cylindrical screen to the
pump suction bell, also shown in Figure 111-22. The cleaning of this
type of screen is very difficult; it may be done by dewatering the bay,
with the use of divers or by backwashing through the pump, all methods
being unsuited to the continuous pump operation required at powerplants.
The bulk of fixed screens are found on smaller and older plants. Some
newer plants located on water bodies that have small debris loadings
have also installed this type of screen. The only advantage over a
conventional traveling water screen is a savings in the cost of the
mechanical equipment and in maintenance costs for the screens, screen
drives, spray wash pumps, etc. Operating costs may be higher if
frequent manual cleaning is required.
Fixed screens have serious drawbacks, both from a plant operation
standpoint and an environmental standpoint. First, operators must be
immediately available to raise and clean the screens when a limiting
head loss occurs (as signalled by a differential level alarm, for
example). Secondly, no matter how light the debris load may normally
be, the possibility always exists that a sudden heavy debris or fish
load could completely clog the fixed screen, causing plant shutdown and
possibly collapse of the screens and circulating water pump damage.
Because of these factors many fixed screens originally installed for
economy reasons have subsequently been replaced with traveling water
screens.
From the environmental standpoint the fixed screen involves longer
impingement periods between cleaning cycles and increased damage to the
impinged fish because of greater velocities across the increasingly
clogged screen. The crude methods employed to clean fixed screens is
also damaging to fish.
59
-------
ID'-i"
o
.y|
FIDE KlkttN-
IdUET-
66T. Of HiUKf—i
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HIU: VM'-J*
T1'
Fill WITH WEI.P
FIU5H WITH TOP
Of i
1 -_.
IS
-^
LV
^
\- »!(.' ft
t Jl»3.t.V-
PET U L HO.
PJXED (STATIONARY) SCREEN DETAIL
-------
HOIST - »
STRUCTURE
"FIXED" SCREENS
2 SETS OF 2)
CIRC. WATER
PUMP
—SERVKE
'WATER PUMP
•TRASH RACK
5TOPLOG5
ALTERNATIVE FIXED
SCRFETN FOR RELATIVELY
SMALL PUMPS
FIXED (STATIONARY) SCREENS
(SCHEMATIC ONLY)
FIGURE 111-22
61
-------
Perforated Pipe Screen
Figure III-22A shows a type of "fixed screen" with characteristics
significantly different from the fixed screens discussed above. The
screen consists of a perforated pipe placed in the waterway and oriented
in such a manner that the passing current will sweep debris downstream.
There are several installations of this type in service. They have to
date been designed for debris handling service without respect to fish
protection. However, it appears quite possible that this type of screen
may be very effective in reducing fish mortality.
Model tests are currently underway for one nuclear powerplant makeup
water intake to develop optimum perforation velocity, size and shape,
all specifically to provide maximum fish protection. Additions to the
inside of the pipe, such as sleeves, may be mads to produce equal
velocities through the perforations. Very low approach velocities can
be achieved with a reasonable total length of perforated pipe, divided
into several individual pipes if necessary. In this manner large
quantities of water may be handled at what may be substantially less
cost and greater fish protection effectiveness than presently used
conventional screens.
Backwash provisions may be included as shown in Figure III-22A, but a
review of existing installations has indicated that these provisions
have not been extensively needed.
Double Entry, Single Exit Vertical Traveling Water Screens
Figures 111-23, 111-24, and IJI-25 show two types of installation for a
vertical traveling screen which takes water from both sides and passes
it out through one end of the screen, thus doubling the screening area
for a given width of screen. Although this unit appears similar to the
conventional traveling screen there are significant differences.
Figures 111-23 and 111-24 show the most common mounting of this type of
screen. The unit is turned so that the approach flow is parallel to the
faces of the screen. It is mounted in a concrete screen well. Water
enters through both the ascending side and the descending side of the
screen, thus utilizing both sides for water cleaning. For a given
theoretical mesh velocity the screen will have twice the capacity of the
conventional screen. There is no possibility of debris carry over to
the pump side, since incomplete cleaning will simply result in returning
the debris to the incoming water for recycling.
There are several drawbacks to this type of installation, however, and
from both the operational and environmental points of view it appears to
be inferior to the conventional screen. Some of these objections are as
follows:
62
-------
PERFORATED PIPE SCREEN
RIVER CHANNEL)
FIGURE IH-22A
63
-------
Guide sprocket
with chain
tensionmg
device, adjustable
with screen
running
Wash water
supply
connection
Non-corrodible
main chains
30,000 Ib breaking
load. Low friction
Nylon rollers
Screen slides
into locating
members
and can be
withdrawn
bodily if
required
OUTLET
Screened
water
DOUBLE ENTRY, SINGLE EXIT
VERTICAL TRAVELING SCREEN
Figure 111-23
Wash water
and debris
chute, tc
drain.
Driving gear
Driving sprocket
Double row of
wash water
fan-|et nozzles
in splash proof
casing
Main frame 'H'
members, with
guide channels
and wearing
strips for chain
rollers
Non-corrodible
screen panels
with deep buckets
for lifting debris,
replaceable without
dismantling
main chains
Fabricated steel
supporting feet,
chain-roller guide
paths continued
in large radius
round base
64
-------
VERTICAL
TRAVELING
SCREENS
A
INFLOW
•4 CIRC. WATER
PUMP5
4- BLANK PLATC
f
VERTICAL TRAVELING
SCREEN'
FACE
I I
\
SPR4Y 5VSTEM
TRA5W TROUGH
5CREEM FACE
^DOUBLE ENTRY, SINGLE EXIT
VERTICAL TRAVELING SCREEN
(SCHEMATIC ONLY)
FIGURE 111-24
SECTION A-A
65
-------
DOUBLE E^'TRY SINGLE EXIT
VERTICAL TRAVELING SCREEN
OPEN WATER SETTING
Figure 111-25
66
-------
a. If the double entry screen is to handle twice the flow volume,
as suggested by the manufacturers, it will have to handle twice as
much debris as the single entry screen. At the same rate of screen
travel debris clogging will occur much more quickly.
b. The clean screen face is first introduced to the flow at the
water surface. The debris picked up by the descending baskets must
then be pulled down and through the boot section. Debris thus
collected on the descending run blocks the screen for the entire
cycle. This is in contrast to the single entry screen which
presents a clean basket to the flew and usually does not encounter
the majority of the debris until just before it lifts out of the
water.
c. Since head loss increases en an exponential basis with the
degree of blockage of the screen wire, the dual flow screen will
have to be designed to operate under higher head losses. Higher
head loss design requires both a structurally stronger screen and a
higher horsepower drive.
d. The double entry screen mounted as in Figure 111-22 requires
abrupt changes in water flow direction as it passes through the
screen. This will result in nonuniform flow across the screen face,
with high localized velocities, additional system head loss and
possibly enough turbulence to upset pump operation.
e. The common setting shown in Figure 111-22 does not provide any
escape route for fish other than to swim back out of the channel.
Definite fish trap areas result at both faces of the screen.
This type of screen is frequently used outside the United States and is
also offered as a standard item by one U. S. manufacturer.
Figure III-25 shows an environmentally promising alternative mounting
for the double entry screen. Here the screen is mounted on a platform
and is surrounded by water on all sides.
There is no confining concrete structure which might trap fish. This is
a major asset from the point of view of fish protection. Trie screen has
some of the mechanical drawbacks of the mounting shown in Figures 111-23
and 111-24. In addition, the pump suction piping will cause non-uniform
flow through the screen mesh since abrupt flow direction changes must
take place to get the water to the pump. Not shown in Figure 111-25 are
trash racks and associated structure which will probably be needed to
protect the screen from heavy debris. Even with such added facilities,
however, the total cost of the screen and pump installation for the open
type mounting may well be less than for an installation using either
conventional traveling screens or the screens mounted as shown in
Figures 111-23 and 111-24.
67
-------
It might be noted here for reference that the principle of the "Open"
type of screen mounting typified in Figure 111-25 is also a feature of
one of the alternative mountings of a European drum screen shown in
Figure 111-38, the pump suction piping is similarly attached to the
screen frame itself, allowing open water to surround the screen, thus
avoiding fish trap areas.
Single Entry, Double Exit Traveling Screens
Figures 111-26 and 111-27 show a screen type which reverses tne flow
path shown for the double entry screen previously discussed. Water
enters through an opening in one side of the screen frame and exits to
both the right and left through the ascending and descending screen
faces. Debris is removed from the screen baskets into a trough on the
inside of the screen by both gravity action and sprays. There is no
possibility of carrying debris over into the "clean" side of the system.
None of these European designed double exit screens is presently in
operation in the United States, but they are en order for at least two
major U. S. powerplants.
The advantages and disadvantages of this design are similar to those for
the double entry screens previously discussed. One potential fish
protection feature of the screen shown in Figure 111-27 is a substantial
debris, water and fish holding trough for each section of individual
curved screen basket. Fish might be less likely to flip out of the
trough back into the incoming water and thus would not be "recycled" in
the manner which is objectionable on unmodified conventional traveling
screens.
Neither this screen nor any of the ether vertical traveling screens were
developed with fish protection in mind. Thus they have tne inherent and
obvious environmental drawbacks which have been highlighted in the
previous discussions.
Horizontal Traveling Screen
Figure 111-28 shows the principle of the horizontal traveling screen, a
device specifically developed to protect fish. It elicits a behavioral
response from the fish similar to the louver diversion system discussed
elsewhere in this report. The horizontal screen, which is still in the
experimental stage, is the single major advance in mechanical screening
technology in the last decade. It was initially developed by the U. S.
Fish and Wildlife Service in Oregon. Later financial and technical
support has come from several utilities and a commercial screen
manufacturer.
As shown schematically in Figure 111-28, the horizontal traveling screen
rotates horizontally at a sharp angle to the incoming water flow. The
68
-------
SINGLE ENTRY, DOUBLE EXIT
VERTICAL TRAVELING SCREEN
FIGURE 111-26
69
-------
INFLOW
TRASH TROUGH-y
f
t •' • *• •
y
' C3
' * '-a -
<: - ° f~ ?• ' "'
-^^~
XREEN
1 1 i ...
N^ ' -* • . ^e • •- . •
.
D
0
*> «.
._..y ..
« o
-------
HORIZONTAL TRAVELING SCREEN
(SCHEMATIC ONLY)
FIGURE 111-28
71
-------
principle is to guide fish to a point where a bypass channel can carry
them to safety. It has been very effective. Upon sensing the screen, a
fish will orient himself perpendicular to the screen and attempt to swim
away from it along VR. This he is able to do since the component of the
channel velocity opposing his effort (VR) is small. In this orientation
the fish is swept downstream along the face of the screen by the
component of channel velocity which is parallel to the screen (VS).
When he reaches the end of the screening leg he moves into the bypass
channel for safe passage back ro the waterway. The size of fish that is
effectively screened can be reduced by reducing the angle of inclination
of the screen with respect to the channel flow direction. However, as
this angle is reduced the size of the screen increases for the same flow
rate, increasing the cost of the intake. Some small percentage of fish
will become impinged on the screen, but they will be released at the
bypass and will also not be pressed as tightly against the screen as
they would be in a vertical screen.
The latest experimental version of this screen (designated Mark VII) is
shown schematically in Figure III-29. It is located on the Grande-Ronde
River near Troy, Oregon and was designed in cooperation with a major
commercial screen manufacturer. Although this screen and its
predecessors have undergone extensive tests the manufacturer and
knowledgeable intake designers estimate that it is at least two
generations of experimentation away from installation at a major steam
electric powerplant. Application of this screen to a large industrial
intake at this time would require extensive and costly research.
Some of the problems are as follows:
a. The screens operate continuously and at very high rates of speed
compared with vertical screens. For the Mark VII screen the rate of
travel is variable from 0.4 to 1.2 m/s (80 - 240 fpm) as compared
with a usual maximum of 0.05 m/s (10 fpm) for the vertical screen.
All components of the mechanism are thus subject to severe wear.
Reliable, long life components have not been developed.
b. Water level differential due to clogging must be limited to
avoid collapse of the screen. Either the pumps must be tripped to
stop flow or the screen panels must be designed to spring open.
This latter solution was used in the Mark VII screen. If the panels
thus open they will release fish and debris and supplementary
conventional traveling screens will be required downstream of the
horizontal screens to protect the cooling water system.
c. The horizontal screen cannot accommodate significant variations
in water depth in its present stage of design. Effective
performance hinges on suitable approach water velocities.
72
-------
:SEAL
FISH AND
.DEBRIS BYPASS
-PANELS NORMALLY
OPEN ON BACKSIDE
PANELS IN EMERG
-OPEN POSITION
PASS DEBRIS
\ OVERLOAD)
SCREEN WIRE--
0-07/ CW DiA-
*8 MESH - 60% OPEW
NET 35% OPEN FOR
OVERALL SCREEN
I STRUCT ELF/1.
SCREEN 1-9
HIGH, WATER
DEPTH
RATE OF SCREEN
TRAVEL, V:
0-4 TO 0-7 m/s
fO HP MOTOR
MARK VII HORIZONTAL TRAVELING SCREEN
(SCHEMATIC ONLY)
FIGURE 111-29
73
-------
d. The maximum screen panel height is about 6.1 meters (14 feet)
due to the same general structural limitations that control the
maximum width of a vertical traveling screen.
e. Due to lack of gradient in the incoming water screen, it is
difficult to obtain sufficient bypass velocity without the use of
supplementary pumps in the bypass system.
f. Debris as well as fish must be handled on the bypass system,
thus required additional water cleaning facilities.
g. Screens would have to be redundant to permit continuous full
load operation during screen maintenance shutdowns. The size of the
installation will thus become very large and costly compared with a
vertical screen facility.
h. Debris and bed load tend to jam lower tracks.
Figure 111-30 is a schematic version of a possible variation of the
horizontal screen setting. This location and orientation would utilize
the velocity of the passing water to carry the fish to safety and remove
trash.
The principle of angling the water cleaning facilities to the incoming
flow is further developed in ether sections, with respect to the louver
system of behavioral guidance and the concept of placing conventional
traveling screens at an angle to the flow.
Revolving Drum Screens - Vertical Axis
At least two types of vertical axis revolving drum screens are in use in
U. s. water intakes, but not in facilities connected with industrial
cooling water systems.
a. The vertical drum revolving in an opening in front of the pumps
as shown schematically in Figure 111-31.
b. The vertical drum revolving around the pump itself as shown in
Figure 111-32.
The screen mesh is placed on a vertically revolving drum. Water level
variations can be handled without difficulty. A vertical jet spray
system can be mounted inside the drum to wash off debris. However, no
convenient way has been developed to move the debris away from the
screen face area.
Figure III-31 shows the drums lined up in such a manner that a passing
river flow will carry away debris and would also carry fish to safety.
Obviously the reliable performance of this system will depend on a
74
-------
TRASH BARS
i:ci
CONTINUOUS
ROTATION
O
o
SPRAY HEADER
FOR TR/A5M REMOVAL
£ CIRC. WATER PUMPS
SCHEMATIC PLAN
ADAPTATION OF HORIZONTAL TRAVELING SCREEN
FIGURE IH-30
75
-------
RIVER FLOW
-TRASH BARS
"SPRAY JET PIPE
FOR CLETANIA/6
I I I I t I I 1 I II 1 M I I I I t I I I t~~1 M I M I ! I I I I | [ I I I I I I I j I 1 1 II 1
PLAN
PUMPS
SCREENS
TRASH BARS
\HI6ti PWATER
LOW.VATER
•••-t-f--
o
TO PLAMT
SECTION A-A
REVOLVING DRUM SCREEN - VERTICAL AXIS
SCHEMATIC
FIGURE 111-31
76
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strong one directional passing current, which is a feature severely
limiting the locations where the screen would be effective. without
such passing flow the debris would simply pile up in front of the
screens. Fish would be scraped or jetted off only to impinge on the
same or adjacent screens.
Figure 111-32 shows the screening element encircling the pump and
revolving around the pump. One major screen manufacturer nas supplied
such screens for relatively small, 0.19 m3/s (3,000 gprn) , powerplant
auxiliary pumps. Another version has been independently developed and
used for an irrigation water intake by the Prior Land Company of Pasco,
Washington. Although this system is experimental and nas been in
operation for only about a year it has served Prior Land's special
needs. The system has had mechanical difficulties, however, and
required major overhaul during the non-irrigation season. Moaifications
and new designs are underway. A vertical spray washing system has been
installed, but no satisfactory provisions have been made to carry the
debris away once it has been washed from the face of the screen.
The screen enveloping the pump must be large in diameter compared with
the bell in order to achieve an acceptable low screen velocity. Only a
small vertical section of the screen will be effective since the flow
lines into the pump bell traverse only a limited area of the surrounding
waterway.
The vertical drum screens described here are not sufficiently developed
to provide protection to fish and appear to be of marginal effectiveness
in handling any but very light debris loads.
Revolving Drum Screens - Horizontal Axis
Horizontal axis revolving drum screens are widely used throughout the
world. There are many variations functioning in quite different ways.
In the United States, however, they have had practically no application
and are not supplied as a standard design for the water quantities
required in powerplants.
A simple drum installation is shown in Figure 111-33. This type of
screen is placed with its longitudinal axis horizontal across the intake
channel. The screening media is located on the periphery of the
cylinder. The screen rotates slowly with its exposed upper surface
moving downstream just below the water surface. Because it operates in
this manner it can be used to separate fish from the water flow with
minimum impingement, if mesh approach velocities are low. Debris is not
removed efficiently.
The important design parameters for the drum screen are mesh size, drum
diameter, drum rotation velocity, and velocities through the screen.
The velocities through the screen are difficult to control since
78
-------
4
Flow/ jo PUMP -£>TB:UC"JV
r-FISH AMD Deb£lS
I COLLECT I OM
C
il
• L
plow ouf
i
I
U I
F to
I
FI5M AUO
fr.•• •»•-•> ^'- •. .•»,f' -v -
—
A-A
REVOLVING DRUM SCREEN HORIZONTAL AXIS
FIGURE 111-33
•SCE.S-B-U
79
-------
portions of the screen are alternately moving with and against the
intake flow. The horizontal drum screen as shown is also sensitive to
water level changes.
Drum screens may be designed as impinging or non-impinging depending
upon the size of the fish to be separated and the velocity of the screen
and the rate of flow in the channel. The impinging design is not
preferable because of possible damage to the fish while on the screen.
It is also difficult to remove the fish subsequent to impingement. High
pressure sprays have been used but these can also damage fish.
No drum screen was found to exist at a U. S. powerplant. Several
horizontal drum screens have been used to divert fish from irrigation
canals. A major installation of this type is the fish bypass structure
of the Tehama-Colusa Irrigation Canal operated by the U. S. Bureau of
Reclamation, shown on Figure 111-34, taken from Reference 21. Since the
water is used for irrigation, debris removal is not as important as at a
powerplant or other industrial intake. Note that the drum screen is
placed at an angle to guide fish to a downstream bypass similar to
horizontal screens and louver diverters. A supplementary pumping system
would be needed to produce the desired bypass flow. There is also a
problem in obtaining good seals at the bottom and against the side
walls.
The advantages of the illustrated drum screen over the conventional
traveling water screens include the decreased number of moving parts and
the possibility of utilizing more than half of the total screen mesh as
effective screen area. However, an industrial intake designed on the
pattern of Figure III-3U would cost considerably more than the con-
ventional intake.
In European practice the term "drum screen" covers a much broader range
of designs. For the purposes of this brief review the terms "drum" and
"cup" are generally interchangeable, depending on each manufacturer's
specific definition. Many of these are used extensively in major
powerplant intakes and are highly regarded for their effectiveness in
water cleaning and their serviceability. None has been designed,
however, with the welfare of fish in mind. A few appropriate
modifications have been made to lessen environmental impact, but in
general this facet of water screening has not been given much attention.
The following types are readily available and often used:
a. Figure III-35, single entry cup screen, where the water enters
at the end (side) of a large rotating drum and passes our through
screen mesh on the periphery. It is limited in size to about 9 m
(30') in diameter because of the cantilever nature of the shaft
support.
b. Figures 111-36 and 111-37, double entry cup screen, where the
water enters the rotating drum from both ends (sides) and passes out
80
-------
(XI
FISH BYPASS STRUCTURE
FIGURE 111-34
-------
DEBRIS REMOVAL SYSTEM
ROTATION
MAXIMUM WATER LEVEL! \1
^\
\\\ MINIMUM WATER LEVEL
SECTION ON A-A
SCREENED WATER
,-t-,
DIRECTION OF FLOW
UNSCREENED WATER
SINGLE ENTRY CUP SCREEN
figure ITI-35
82
-------
DEBRIS REMOVAL SYSTEM
ROTATION!
SCREENED
WATER
SCREENED
WATER
DOUBLE ENTRY CUP SCREEN
Figure 111-36
83
-------
DOUBLE ENTRY CUP
SCREEN
OUTLET
SCREENED
WATER
SCREEN STRUCTURE WITH
DOUBLE ENTRY CUP SCREENS
Figure 111-37
84
-------
through the mesh on the periphery. These screens have been made as
large as 18.3 m (60') in diameter. Efforts have been made to
provide oversize debris lifting buckets to carry fish in water up to
the debris removal system and trough at the top of the drum travel.
c. Figure 111-38, a double entry drum screen where the screen mesh
covers the ends (sides) of the drum and the periphery is closed.
Water enters the sides and also leaves one side through a pipe
around which the drum rotates. This screen rests on piers without a
surrounding concrete structure, a mounting which permits water flow
around all sides and which thus provides escape routes for fish. In
this respect the setting is similar to the double entry vertical
traveling screen offered by a U. S. manufacturer and shown in
Figure 111-25. Screens of this type cannot be cleaned efficiently
because of the tendency for the debris to fall back into the raw
water as the screen rises.
The structure required to mount drum or cup screens is substantially
larger and more costly than the vertical traveling screen structure
designed to handle the same quantity of water under the same conditions.
They are reputed to be easier to maintain (the horizontal shaft is
located above normal water level), there are fewer mechanical parts and
there is no possibility of carryover of debris into the circulating
water system.
Rotating Disc Screen
Figure 111-39 shows a typical rotating disc screen, a type which is
suitable only for relatively small flows and small water level
variations. The screen mesh covers a flat disc set at right angles to
the water channel. The disc rotates around a horizontal axis, bringing
the dirty screen face above water where high pressure sprays wash the
debris into a trough similar to that used for conventional traveling
screens. It has a minimum number of moving parts and is thus
inexpensive to buy and maintain. The circular screen shape makes
inefficient use of available area of the incoming water channel. No
more than about 35% of the total screen face is being used at any one
time.
Such a screen has no advantage over other common screens from the fish
protection point of view. It also has most of the drawbacks, including
probability of fish impingement, the need for high pressure sprays to
remove fish and debris and the need for a very large screen structure to
limit screen approach velocities to those now being considered for fish
survival.
85
-------
5ECTIOU A-A
DOUBLE ENTRY DRUM SCREEN OPEN WATER SETTING
FIGURE III-38
86
-------
Rotation
Access platform
if required "-
Electric drive
unit
Screening panels
ROTATING DISK SCREEN
BASIC ELEMENTS
ROTATING DISK SCREEN
IN OPERATION
Figure 111-39
87
-------
Miscellaneous Mechanical Screens
Water treatment plants, sewage disposal facilities and various
industries requiring service water employ many other configurations of
mecharical screens, strainers and filters. Many are designed for much
smaller water flows than are required fcr powerplant circulating water
systems. TVS with most of the screens described in this section they
were designed specifically to produce screened water, nor to protect
fish. consequently, they do not have features we feel are worth
considering for incorporating into facilities being designed with fish
protection as a major criterion.
In addition to the screening device, other types of systems can
influence the design of intake structures. The need for fish bypass
systems ir. conjunction with some of the screening systems nas been
discussed in previous sections. Fish handling and bypass equipment can
also be used to return impinged fish back to the waterway. Relatively
little work has been done on developing these facilities for
incorporation into existing industrial intakes. Most of tnese types of
facilities have been installed at irrigation diversions operated by the
U. S. Bureau of Reclamation and the State of California. A great deal
of work has been done in the Pacific Northwest in diverting salmon
around hydroelectric impoundments. As more powerplant intake designers
become aware of the need for fish handling and bypass facilities, they
will have a greater impact on the intake configuration employed.
Fish bypass and handling facilities of interest include the following:
fish pumps
fish elevators
"crowding devices"
bypass conduit
modifications to vertical traveling screens
Fish Pumps
Fish pumps have been used for many years. The rotary type of pump with
open or bladeless impellers seem to cause the least amount of damage to
fish. However, all rotary pumps are not necessarily suitable for
pumping all types of fish.. The use of hydraulic eductor pumps was
thought to be ideal for fish pumping. However, fish passing through
such eductors encounter high pressures which seem to cause more damage
than mechanical pumps 13.
88
-------
Fish Elevators and "Crowding Devices"
Several types of bucket elevators have been tested in elevating fish on
a batch rather than a continuous basis. One such system was tested at
the Tracey Pumping Station by the National Marine Pisneries Service in
conjunction with the horizontal traveling screen. This system is shown
in Figure III-40. The fish are first concentrated over the lower bucket
by use of a crowding device and then raised and dumped into -trie fish
trough for bypass. This type of system might be quite useful at intakes
where fish might congregate in quiescent zones created by such things as
curtain walls and other intrusions into the screen channel.
Fish Bypass and Transport Facilities
After being concentrated and removed from the screen well, tne fish
require a means of conveyance back to a hospitable environment the
waterway. The design of the bypass system should minimize the time that
the fish is out of water and insure safe and rapid return to the
waterway at a location sufficiently removed from the intake to prevent
the recirculation of fish and reimpingement. Once the fxsh have been
raised to an elevation above that of the waterway they can be discharged
to a trough or pipe for gravity return to the waterway. Care must be
taken in the design of the fittings and elbows of the discharge conduit
to prevent undue stress on the fish. Furthermore, discharge of fish
should be made to a hospitable environment.. Considerable experience in
designing and operating long fish bypasses for both upstream and
downstream migrant salmon has been obtained in the Pacific Northwest.
The technology exists for these types of systems. Where conditions do
not permit direct hydraulic conveyance, fish can be trucked back to the
waterway. Trucking fish over Icng distances does not seem to cause
unacceptable mortalities. Both trucking and airlift nave been used for
seeding waterways with fish. Reference 13 has some suggested criteria
for trucking fish.
Modification To Existing Traveling Water Screens
The fish bypass facilities described above were intended to remove fish
from the intake structure to prevent impingement. An interesting
example of modifying an existing traveling water screen to bypass
impinged fish is described below.
The installation is a major nuclear station on the eastern seaboard
(plant no. 5111). The station is located above the river and 2.7
kilometers (1.7 miles) from the intake. Water is pumped from the river
into the "high level" canal from which it flows by gravity to the
screens located at the plant. Apparently juvenile fish pass through the
pumps and become entrapped in the canal for subsequent impingement on
the screens. The first modification made was to connect the screen
waste flow to the plant discharge canal using a 45 cm (18") polyethylene
89
-------
FISH TROUGH
g-i m
2-1 W DEEP
:SCREEN WASH BAR - SINGLE BAR
FISH BASKET COLLECTION SYSTEM
FIGURE DII-40
90
-------
pipe. Tests made on the system in this condition, showed that this
transport system minimized mortality when the screens were operated
continuously during the cold water period but that damage was above
acceptable levels during the summer. Mortality was primarily caused by
high screen wash water pressure and by recycling of fish at the air-
water interface of the screen front. It was concluded that "recycling"
was a higher mortality factor in the summer than in the winter because
tha more active fish would flip back into the water after the screen
basket cleared the water surface and be reimpinged. Tnis would be
repeated until the fish were dead or weak enough to remain on the narrow
lip until the basket reached the wastewater stream.
The modifications are shown schematically in Figure 111-41. They
consisted of bolting a 10 gauge steel trough on the lip of the
conventional screen baskets. The troughs were positioned to maintain a
minimum of 5 cm (2") of water depth during the time of travel between
the water surface and the head shaft sprocket. The new screens are
designed to be continuously operated, thus reducing the time of any
possible impingement of fish on the screen to two minutes or less.
The screen wash system was also modified to minimize damage caused by
the standard high pressure jets. As the screen travels over the head
shaft sprocket, the fish will be spilled onto the screen surface. On
further rotation, fish will slide down the screen and be deposited into
a trough of running water for transport back to the river away from the
intake structure. A low pressure screen wash system has been
incorporated into the design to aid in removing crustacians and
returning them to the river.
Since these modifications are only now being installed at the plant, no
data on the performance of these modifications are available. No prior
model testing was performed and a prototype will be used to verify the
capabilities of the system. If reasonable efficiencies in bypassing
fish safely are obtained, this type of system might be utilized to
modify other intakes where impingement is a problem. The system could
be installed on most existing conventional intakes, and the cost is
roughly 30% of the intial screen cost plus the cost of the bypass line.
The intake is not substantially changed.
One disadvantage of this system may be a lack of acceptance on the part
of some of the regulating agencies. We noted a problem regarding
discharge of debris after it has been removed from the waterway. As can
be seen from the figure, there is no way to avoid discharging a portion
of the debris in the fish bypass channel. Stringent resrrictions may
prevent the use of this system at many locations.
91
-------
LOW PRFSSURE JETS
FOR
/O DISCHARGED 1
QUQHS — • — <* i
•*• r
c
i
t
S1 ^
^\
j
d ijiru pRrsc.(yRF JFT
3 FOR RFftPK RFN|/
. , _*' ^ n CT i M c i r~ p1 T" r\ \ i T~
LDUNMo UL.' i (JU I
1 WHICH HAS OTHER
, ex DOWNSTREAM)
3 ><="* 1-LOW
^--U> V~ FI5M
"5
DUAL
AT SURREY,
SCREE/MS
FALL OFF1
SECTION
SCREEN FACE
^*.-— -—
\ fA POOR FEATURE)
\
FRONT OF 0A5KET
KIGW TO KEEP
FISH IAI
IO-5*
:FISH RENOVAL
DETAIL
BASKET DETAIL
MODIFIED VERTICAL TRAVELING SCREEN
FIGURE 111-41
92
-------
Intake Structure Designg
In addition to special biological considerations, the size and shape of
an intake structure should be determined to a large extent by the
following factors:
The quantity of intake flow
The type of screening system used and allowable water approach
velocity
The relationship of the intake to the water source
Miscellaneous factors such as need for storm protection, avoidance
of excess sedimentation, ice control
Since most existing powerplant intakes employ the conventional traveling
water screen they will be referred to as "conventional" intakes,
implying that they are equipped with such a screen.
Conventional Intakes
There are three general classification of conventional intake structures
based on the relationship of the intake to the water source. These are
as follows:
Shoreline intake
Offshore intake
Approach channel intake
Shoreline Intake
The most common intake arrangement is the combination of inlet, screen
well and pump well in a single structure on the edge O£ a river or lake.
The best designation for this installation is "pump and screen
structure", to clearly distinguish it from individual structures also
commonly used. A plan view of this type of structure is shown in Figure
111-42. A cross section of the shoreline structure is shown in Figure
III-U3. Note that the water passes (in order) the trash rack, the stop
log guide and the traveling water screens on its way to the pumps. This
type of structure is used where the slope of the river bank is
relatively steep and there is relatively little movement of the water
edge between high and low water. A variation of shoreline structure
design is shown in Figure 111-44. Here a skimmer wall is used to insure
drawing in of cooler lower strata waters. Curtain walls, used primarily
to protect trash racks and screen from logs and ice, can also be used to
draw in cooler water.
93
-------
4-
5HORELINE7
i
LAKE
OR RIVER
PUMPS
j-PIPELINE
.WATER SCREENING
FACILITY
PLAN
SHORELINE PUMP AND SCREEN STRUCTURE
FIGURE 111-42
94
-------
Mech Trash
Rake
Screen _»
Wash Pump
CONVENTIONAL PUMP AND SCREEN STRUCTURE
FIGURE 111-43
95
-------
ROTATING SCREEN-/
TRASH BAP5-
, WATER
PUMP
TO PL4NT
H.W
L.W
SKIMMER WALL.-*-
LOW LEVEL
INTAKE
7/>/X '^T
PUMP AND SCREEN STRUCTURE WITH SKIMMER WALL
FIGURE 111-44
96
-------
Offshore Intake
The offshore design separates the inlet from the pump well. This type
of intake is used where there is a significant lateral movement in the
waterway between high and low water where there is a particular
technical or environmental reason for utilizing the water supply at a
distance from shore. Figure 111-45 and 111-46 show two similar concepts
of such an intake. The design shown in Figure III-46 employs a siphon.
The term siphon here refers to a gravity pipe placed above the level of
the water and thus flowing under vacuum. The prevision of fine
screening facilities at the ccnduit inlet offshore is often impractical
because of construction difficulties, because of the navigational
hazards it presents or because of difficulty of access for operation and
maintenance. Therefore, the fine screens are usually located in a shore
structure as shown in both Figure 111-45 and 111-46. Flow velocities
are commonly rather high (say 1.5 to 3.0 mps) in the inlet pipeline to
reduce its cost and most species of fish would not be able to escape
entrapment in the system after entering it. Therefore a considerable
amount of interest centers on the inlet structure as the place to guard
against fish entrapment in an offshore intake. Since offshore intakes
can have screens onshore, diversion weirs or crowders can be used as a
second line of control to remove fish prior to possible interaction with
the screen.
Approach Channel Intake
In this type of intake, water is diverted from the main stream into a
canal at the end of which is the screening device. Tnis type of intake
is shown in Figure 111-47. Channel intakes have often been used to
separate the plant intake and outfall for the control of recirculation
effects, to permit location of the pump structure where it can more
easily be constructed or to reduce total system friction losses and
costs by replacing high friction, high cost pipe with lew friction, low
cost canals. It may also be used to remove the intake from the
shoreline for aesthetic reasons which are discussed elsewhere. Fish
will tend to congregate in these approach channels and tnus increase the
incidence of entrapment at the screens. A modification of the approach
channel concept is shown in Figure 111-48, where the screen structure
has been placed at the entrance to the channel and becomes essentially a
shoreline intake, without the fish entrapment hazards inherent in the
channel scheme. However, care must be taken with the shoreline intake
to avoid velocities which could increase impingment.
Conventional Intake Design Consi derations
In addition to special biological considerations, other important
considerations in the design of conventional pump and screen structures
are the following:
97
-------
ROTATING SCREEN-
TRASH BARS -
V1EAD LOSS IN
INLET PIPE
TO]
CIRC. WA7TR
PL/MP
V
FISH CAP
(VELOCITY CAP)
TO PLANT
PUMP AND SCREEN STRUCTURE WITH OFFSHORE INLET
FIGURE 111-45
98
-------
vc
vc
SIPHON INTAKE
RIVER OR
'.. LAKE-
i
PRIMING
CONNECTION
SCREEN
*
V
-PUMP
PROFILE THROUGH WATER INTAKE
SIPHON TYPE
FIGURE 111-46
-------
OUTFALL
GENERATING
PLANT
LAKE
APPROACH CHANNEL INTAKE—^
APPROACH CHANNEL INTAKE
FIGURE 111-47
100
-------
Lake
or
Rivet
r
Water Screen Facility
(Example 2)
^ P-4
"^"Channel
O-
OM
M
O
Pump Well
SCREEN LOCATION - CHANNEL INTAKE
FIGURE IH-48
101
-------
water level variations
Inlet design
Screen placement
Screen to pump relationships
Flow lines to the pump and the pump chamber configuration
ice control provisions
Access to the structure for operation and maintenance
Inlet safety design considerations will be different for each of the
three classifications of conventional intake structures. For the
shoreline intake an important consideration is to avoid significant
protrusions into the waterway. This is shown diagramatically in Figure
111-49. The top sketch shows an example of undesirable intake design
where the side walls of the intake structure protrude into the waterway
and create eddy currents on the downstream side of the intake. Fish are
sometimes found concentrated in these areas, a situation which may
increase the possibility that they will become entrapped in the intake.
The bottom sketch shows a more suitable design with no portion of the
intake structure protruding into the flow. Of course, this would not be
significant at structures drawing water from a lake shore location where
cross flow velocities are negligible.
Screen Placement
Most conventional intakes are designed with the traveling water screens
set back away from the face of the intake between confining concrete
walls. As shown in the top sketch of 111-50, this creates a zone of
fish entrapment between the screen face and the structure entrance.
Small fish will not swim back out of this area. The bottom sketch of
the same figure shows an alternative screen placement with screens
mounted flush with their supporting walls. The trash rack facility is
so designed that there is an open passage to the waterway directly to
both left and right of the screen face. In this design, there is no
confining screen channel in which the fish can become entrapped.
Figures 111-51 and 111-52 show two recent designs of "flush" mounted
screen structures. The first is the screen and pump for a major fossil-
fueled plant in the Northeast (plant no. 3601) . Figure 111-52 is the
pump and screen structure for a major fossil-fueled plant on the west
coast (plant no. 0610). Note that the screens are mounted flush with
the shoreline in each case and that fish passageways are provided in
front of the screens. In these designs there is no provision for stop
logs to permit dewatering the screen wells. Extending the screen
support walls to provide stop log guides would defeat the "flush"
mounting principle.
102
-------
RIVFR FLOW
SCREENS
SHORE LINE-
-> -h-i+) --
PROTRUDf/NG
- WALL
-AREA OF WATER EDDIES
PUMPS
POOR DESIGN
RIVER FLOW
SHORE UNE-
PUMPS
GOOD DESIGN
SHORELINE INTAKE STRUCTURE
FIGURE IH-49
103
-------
Bars
Screen lVe//s
(ilsh ehtrapmen't areas)
Sharel/ne.
i 1 1 1 j 1 1 ni 1 1 1
x
X
x
1 1 1 1 ! V 1 1 \
Scrzer
TTTTTLI~Xin I I I I INITTTI~
CONVENTIONAL
Pumps
Trash Bars
MODIF/ED ScKEEN
(FLUSH MOUNTED
FIGURE 111-50
104
Screen
umps
-------
o
Ul
Trove lino
Trash Rake
Travel/no
lo ower P/chi
!2 It ID. Ccnc
\
IP
(I"
%
PUMP AND SCREEN STRUCTURE
FIGURE ni-51
-------
•BAY-
UMUliiililJ ;J!UliL^a;iLiiiliiUJJi]lUi I ti
tH <-' U U u
L )
SCREENS FDR
UNITS 5 i 6
NOT SHOWN
,-_/-,_/-,.__
;®
/'
•TRASH RACKS
TRAVELING SCf-:
WV/GMALL
n
©t-
££/••//, TERING
5': OP LOG
LOCATION
\^p!JMps T0 UNIT5 i ro 4
SECTION- PLAN
MHWL+3.Z
TRAVELING SCREEN
PUMP
SECTION- ELEI/ATION
PUMP AND SCREEN STRUCTURE
FIGURE 111-52
106
-------
Where channel sections leading to the screens cannot be avoided due to
some unusual condition, proper design of the screen supporting piers can
reduce the fish entrapment potential of the area. This design
consideration is shown in Figure III-53. In Figure III-53A an example
of incorrect pier design is shown. The pier which protrudes into the
flow presents a barrier to fish movement. They cannot make the turns
required to escape the screen. Figure III-53B shows a much more
suitable design. With the extended portion of the pier eliminated, the
fish can move sideways and rest in the relatively still water near the
face of the pier.
Maintaining Uniform Velocities Across the Screens
It is essential in good screen structure design for environmental
protection to maintain uniform velocities across the entire screen face.
When flow is not uniform across the screen, the potential for fish
impingement is increased.
Figure 111-54 tabulates a typical run of a model test series made for a
major plant in the northeast (plant no. 3601). The variation in
velocities is evident. Flow distribution in many existing intakes is
much less uniform than indicated in Figure 111-54.
There are several ways in which a non-uniform screen velocity can be
created. Figure III-55 illustrates some of the factors which create
non-uniform velocities in the screen area. Sketch A of Figure 111-55
shows the condition when water approaches the screen structure at an
angle. Flow tends to concentrate at the downstream side of the water
passage entrance and in some cases may even flow backwards on the
upstream side. Sketch B shows the effects of curtain walls projecting
into the water passage. Curtain walls similar to that shown here are
frequently used to reduce the intake of surface debris or to confine the
entering water to a lower and normally cooler strata. The result is not
only the creation of non-uniform velocity conditions at the screens, but
also the creation of a dead area where fish may become entrapped. They
will not usually swim back to safety under the wall. Sketches C and D
show the effects of pumps or downstream water passages so located that
water is drawn from a limited horizontal or vertical strata as it passes
through the screens. Pumps or gravity exit pipes may be too close to
the screen or may be offset from the screen center. Hydraulic Institute
standards recommend a minimum distance" from screen to pump, but this
distance is established for suitable pump performance, not for best
utilization of the screen area.
The obvious result of the poor distribution of flow through the screens
is the creation of local areas of flow velocities much higher than the
calculated average design velocities. Entrapment of fish is thus
increased.
107
-------
SCREE&L
I
IUNDESIRABLE
FISH CANNOT -
MAKE TURN IN
THIS AREA
FIGURE A
UNSATISFACTORY DESIGN
If
SCREES'
X
_4-
t
RSH
JN TH
REST
5 AREA
\
FIGURE B
IMPROVED DESIGN
PIER DESIGN CONSIDERATIONS
FIGURE 111-53
108
-------
Velocity meosurements ( In ft/sec ) at entrance
of pump Bay No. 3 for the following conditions!
Pumps 1, 2 and 3 In operation; 2 ft/sec river
flow with the water level of 0' , and full wall
openings.
First cross-section ( upstream from the frash-rolce )
(a) (b) (c) (d) (e) (0
NearBottom 0.34J 1 .06 \ 1.12? 0.74\ 0.95 1 0.75 f
0.45! 0.93 t 1.02\ 0.89 \ 0.75 \ 0.83/
0.57\ 0.67 t 0.33 f 0. 41 / 0.31 f (nil)
Mid-Depth
Near Surface
Second cross-section ( In the flshway )
(a) (b) (c) (d) (e) (0
NearBottcxr, 0.39* 0.57\ 0.99t (nil) 0.75t 0.73 1
Mid-Depth (nil) 0.57 1 0.95 1 (nil) 0.90 1 0.80 t
Near Surface 0.62t 0.68 / 0.87—0.77*0.95-0.72-
Third cross-section ( downstream from the screen)
(a) (b) (c) (d) (e) (0
Near Bottom 0.68t 0.84 f 0.80 t 0.60t 0.74 t 0.67 t
Mid-Depth O.BOt 0.95 t 1.06t 0.67to.8ot 0.81 t
Near Surface 1 .20t l.Olt 0.47 t 0.63 1 0.63 t (nil) t
CIRC WATER
PUMP
'•• °o" 1"*" *
)
TRAY
SCREEN
"yf"
HN _
LU
Ul
BAY *3
B E
°"-^ •* .. *
O -
tn
SCREEN AREA VELOCITY DISTRIBUTION
FIGURE 111-54
109
-------
e-
FISH ENTRAPMENT
AREA-7
PUMPS
GRAVITY PIPE
TO PUMPS AT PLANT
LJ
UJ
cn
1 H ^
i Lu =c
LL C-£
Lu ui
UJ
•TO
FACTORS CONTRIBUTING TO POOR FLOW DISTRIBUTION
FIGURE III-55
110
-------
One basic consideration in initial layout of the structure is the
matching of the pumps to the screens. Figure 111-56 illustrates four
intake variations to accommodate pumps of a wide range of sizes. Sketch
A is an intake for several small pumps served by one screen. The shape
is produced by the fact that the flew required by the pump is so small
that only a minimum sized screen is required. Sketch B is a one pump -
one screen arrangement common for medium size pumps up to about 100,000
gpm. Beyond this pump size the physical limitations on the screen size
(14 foot trays or baskets are the maximum commercially available)
requires the use of multiple screens per pump. Sketches C and D
illustrate possible combinations. Care must be taken to locate the
screen with respect to the pump in a manner which will properly utilize
the entire screen surface. If a very low screen velocity is required
for a very large pump installation, the length of structure required for
the screens may be greater than that which will be hydraulically
suitable for the pumps. Such a requirement could result in the
configuration shown on Figure 111-57.
Pump Runout and the Effect on Screen Settings
Sketch A of Figure III-58 shows a typical one screen per pump intake.
If the screen is sized for the design flow of the pump, the screen
velocities will substantially increase during periods when only one pump
is in operation. This is the result of the "runout" characteristics of
the pump which tends to pump more water as the total system flow and
head losses decrease. As much as 40% flow increase might be expected.
Operation in this manner is common in those areas where winter water
temperatures are much lower than summer temperatures. We may then
expect an increase in screen velocity during those cold water periods
when lethargic fish might be least able to resist the flow.
consequently, if this type of setting is used, the screens must be
designed for the expected runout flow of the pump.
An alternative to the individual bay setting shown in Sketch A is to
place the pumps as shown in Sketch B of Figure III-57. In this case, an
open chamber is located in the side wall between the pumps and the
screens. The operating pump may thus utilize a part of the screen area
normally used for an adjacent pump. Field and laboratory tests show
that only a small part of the adjacent screens are effectively utilized
in this situation, but that a small part will be sufficient to
compensate for the increase in pump flow if the screens and pump are
properly located.
An intake of the latter type will be larger and more costly than the
former. Maintenance procedures may be complicated by the fact that the
central bay cannot be dewatered and also the dewatering of individual
screen and pump bays becomes more complex.
Ill
-------
Screen
Pumps
Screens
umps
Screens
B
o
o
o
Pumps
D
Screens
PUIT
PUMP/SCREEN RELATIONSHIPS
FIGURE 111-56
112
-------
SHORE" LINE
PUMPS
PUMP AND SCREEN STRUCTURE FOR LOW INTAKE VELOCITIES
FIGURE 111-57
113
-------
A
B
EFFECT OF PUMP RUNOUT
FIGURE m-58
114
-------
Design of Ice Control Facilities
Most powerplant intakes located in the northern latitudes must have some
provision for ice control during the winter months. Sheet ice and
"frazil" ice ("needle" ice) can cause flow blockage at the intake. The
system most frequently used to control the ice problem is the
recirculation of a portion of the v;armed condenser water back to the
intake. Figure III-59 shows a cross section of a powerplant intake with
the ice control header and discharge ports located upstream from the
screens. A variation of this method would be to recirculate only
intermittetly to minimize fish retention at the intake area. The sketch
shown is for a major nuclear plant located on the Mississippi (plant no.
3113). Other ice control systems that have been tried have been less
successful. In particular, several attempts to use an air bubble
curtain (similar to that described in the section on behavioral
screening) to control ice have not been completely effective. Other
methods of ice control are to place the intake well below the water
surface, or, for sheet ice, to agitate the water surface with propellers
or similar devices. The problem with the use of the recirculation
system for ice control is that it has been shown that fish concentrate
in warmer water in the winter time, thus increasing their possible
interaction with the screen. It has also been shown that fish are
lethargic in the cold water periods and cannot swim well against the
intake flow. These two factors can combine to make the traditional warm
water recirculation system less than desirable from an environmental
standpoint.
It is suggested" that traditional warm water recirculation systems be
avoided. While the feasibility of other ice control systems is yet to
be proven at major powerplant intakes, there does not appear to be any
technical limitations to the development of alternate ice control
systems.
Non-Conventional Intakes
Non-conventional intakes vary considerably from conventional intakes in
that they will use methods for separation of water and debris other than
the screening devices and/or screen mountings previously mentioned. The
non-conventional intakes to be described in this section include the
following:
Open setting screen
Filter type intake
Perforated pipe intake
Radial well intake
115
-------
SLUICE GATE
OPERATOR
MAX. H.W
TRASH
RAVELING RACK
SCREEN-
L.W FROM PLANT
"DISCHARGE* SYSTEM
-ICE ^
CONTROL
TUNNEL
L.L.W
SLUICE GATE (FOR
V/ARN
RLCIRCULATION
.- LADDERS
STOP LOG" GUIDES —
PUMP AND SCREEN STRUCTURE WITH ICE CONTROL FEATURE
FIGURE ni-59
-------
Open Setting Screens
Figures 111-25 and 111-38 shew two screens which have been mounted on
platforms and connected directly with the pumps which they serve. One
is the double entry, single exit vertical traveling screen, the other
the double entry drum screen of European design. Both of these
screening systems have open water completely around them, thus
eliminating fish entrapment areas. A second advantage of rhese systems,
and the original purpose for which they were developed, is the
elimination of costly concrete screen wells. Most such installations
would require some type of trash rack protection which is not shown on
the figures.
Flow distribution through the screen faces may not, however, be suitably
uniform. The areas nearest the inlet to the pumps will tend to have
higher flows and velocities and may therefore result in undesirable fish
impingement. This objection might be overcome with internal dividers
and increased screen sizes, but no information is available that
indicates that such measures have been utilized.
A similar system is being used at plant no. 1229 located on the
southeast coast. The system has performed reliably for several years.
Filter Type Intake
Many types of filter intakes have been developed on an experimental
basis and some have been installed in relatively small scale
applications for powerplants. The essential feature of all these
schemes is the elimination of mechanical screens. The water is drawn
through a filter medium such as sand and stone. Such an intake is
capable of being designed for extremely low inlet velocities and can be
effective in eliminating damage even to small fish. Planktonic or-
ganisms can also be protected to some extent.
Figure 111-60 is a sketch of a stone filter in use since late 1971 to
screen makeup water for a large powerplant in the northeast (plant no.
4222). The sketch shows the original filter. It has since been
modified several times in attempts to improve its performance. It still
has a tendency to clog and cannot yet be considered reliable. Figure
111-61 is a somewhat more complex design developed but not used for the
makeup water of a large powerplant in the Northwest (plant no. 5309).
A preliminary filter design has been developed for the entire
circulating water flow to serve a major powerplant in the Northwest
(1,500 cfs). This system employs precast concrete filter modules in
seven separate filter sections, each capable of being isolated for
maintenance. The entire filter complex would be about (450 x 260 feet)
in plan. Fairly complex piping, water control and pump facilities
complete the system.
117
-------
I MAX , y/PiPE
FFV-.
INFILTRATION BED INTAKE - PLANT NO. 4222
FIGURE ni-60
118
-------
Another filter system concept which has been used with seme success in
relatively small intakes is the "leaky dam" which consists simply of a
stone and rock embankment surrounding the pump structure. Water must
flow through the "dam" to reach the pumps. The dam thus acts as a
screen. Very low water passage velocities can be achieved and the
danger of fish impingement is reduced. Very small fish can, however,
pass through the openings in the stone. A major problem for this system
in waters containing suspended matter would be clogging. Practical
backwashing facilities have net been developed. An intake system of
this type has been operated at powerplant no. 5506 since late 1972. It
has been reported be 70-75% effective in screening out fish.
Although these filter intakes would appear to be ideal from an
environmental point of view, they have many disadvantages. The clogging
problem is foremost. In turbid waters such clogging would rule out the
filter use. Backwashing facilities will be needed in even relatively
clear water. The backwashing procedure will temporarily raise the
turbidity of downstream waters and thus may be in conflict with
limitations on turbidity. To date no large scale filter system has been
developed and proved reliable in operation. The cost of such a system
will be substantially higher than for a comparable conventional screen
facility.
Perforated Pipe Intake
A typical perforated pipe intake is shown in Figure Ill-bl and 111-62.
This concept has been discussed in detail under "fixed screens"
elsewhere in this report. The figures show a preliminary design being
considered at this time for the makeup water system of a major steam
electric powerplant in the Northwest (plant no. 5309). The concept can
be expanded to handle substantially greater quantities of water than the
25,000 gpm to be passed through the illustrated intake. See the
previous discussion for a review of the advantages and disadvantages of
this scheme.
Radial Well Intake
The radial well intake is an infiltration type utilizing natural in-
place pervious material as contrasted with the artificially prepared
filter beds discussed above. Slotted pipes are jacked horizontally into
sand and gravel aquifers beneath the river bed. These pipes are
connected to a common pump well. This is an intajce which has been
frequently used for obtaining highly filtered industrial and municipal
water. The radial well intake is shown in Figure 111-63. Tnis type of
intake can only be successful where suitable water bearing permeable
material is found. It provides a degree of screening which far exceeds
the requirements for cooling water supplies. It has the advantage of
being the most environmentally sound intake system because it does not
119
-------
FILTER CAPACITY 25,O
("3 CC-'-LS IN OFEHATi^N,2 CELLS
E-ACKWA5HING)
PUMP STRLJCTUKiT:
TYP TiuTC-K (
i"- 10' t
^;-,,,,^Yr^- --'"V-3
^ *£ ^'" I o' i r' - p
INFILTRATION BED INTAKE - PLANT NO. 5309
FIGURE ni-61
120
-------
• PUVPHOUSE
BACKWASH PIPE
GATE-
•f3 • 12,500 GPV)'
I
\ —
->
_______
_.
-
— • — .
^---
I
+^*
WAXIM'JM FLO
^ CA!
MORMAL HIGH
EXTREME LOW
~2 FT I
AI3SON
$1 1/2 rr
i r r
-900FT-
PERFORATED PIPE INTAKE
FIGURE ITI-62
-------
PT.AN
"Pumps
o
o
CM
0
-p
a
D
'
_A a
-
Ground
r_
Leve_l
**"
r
i
j —
-A
^
j
^
A
_
P
r
,
\
1
L
x^
~^^Li
f \^^ River
/v--^. ^
Reinforced ' |
Concrete
Caisson
Sand and Gravel Aqui
i —
Perforated Screen
Pipe Jacked into Aquifer
j
Section
RADIAL WELL INTAKE
FIGURE 111-63
122
-------
have any direct impact on the waterway. It would be competitive in cost
with conventional small intakes of the same capacity. However, for very
large capacity requirements, several individual widely scattered cells
would be required and the cost would be substantially greater than for a
conventional intake. Radial well intakes have been in service for over
35 years and have been reliable.
Behavioral Intakes
The wide variety of behavioral intakes has been discussed elsewhere in
this report. They represent a substantial departure from "conventional"
screen facilities. Such intakes include horizontal screens, louvers,
air bubbles, sound, etc., and combinations of these features with each
other and with more conventional facilities.
Conventional intakes themselves can be modified to take advantage of
fish behavior. For example, angling conventional screens to the
incoming water flow can guide fish to bypasses in the same manner as the
horizontal screen and the louvers. Figure 111-64 is a sketch of such an
installation. The total facility will be substantially more costly than
the more conventional setting due to the orientation of the screens and
the need for providing fish bypass facilities (including fish pumps and
auxiliary water cleaning equipment). Hydraulic studies can be made to
develop guide walls both in front of and behind the screens to assure a
reasonably uniform flow through screens.
123
-------
r-
en
o
m
S
CN
r-
-------
SECTION IV
CONSTRUCTION
In t ro due t ion
The adverse environmental impact associated with the construction of
cooling water intakes results from three factors. The first of these is
that the intake may occupy a finite portion of area in the bed of the
source water body. To the extent that this occurs, there will be a loss
of potential habitat and a displacement of the aquatic populations that
reside at that location. In addition, modifications to a larger area
surrounding the specific intake location, resulting from construction
activities and changes in existing topography can create permanent
disruptions in the biological community.
The second factor is the irrpact on the ecosystem of increased levels of
turbidity resulting from the construction of the intake structure and
any associated inlet pipes and approach channels. Turbidity levels can
also be increased as the result of ercsion of inadequately protected
slopes of excavations and fills created during the construction
operations.
The third factor concerns the location of disposal areas for the
materials excavated during construction. If spoil disposal areas are
located within the confines of the source water body, further permanent
disruptions of the existing aquatic species can result. If these spoil
banks are not adequately stabilized, increased levels of turbidity may
persist for an indefinite period. Adequate protection and stabilization
of spoil areas located above the waterline are also required to prevent
long term erosion of these materials which can contribute to increased
turbidity levels.
Of the three factors mentioned above, the first will not significantly
impact the environment in most cases and will be discussed briefly. The
remaining two factors can create serious short term and long term
problems if not properly controlled.
Displacement of Resident Aquatic Organisms
The impact of the physical size of the intake on the displacement of the
resident biological community is a function of the size of the intake.
Offshore intakes which require long conduits placed in the waterbody
will be more disruptive to the resident species than shoreline intakes.
The species that will be most effected by the construction of the intake
are the benthie organisms. The impact of construction activities in
this regard is expected to be small since in no case will the intake
occupy more than a small percentage of the total area of the source.
All water sources will be able to adjust rapidly to the loss of habitat
125
-------
area and to reproduce the small portions of the important organisms
lost. If the locational guidelines proposed are followed, the impact of
this aspect of intake structure construction will be minimized.
Turbidity Increases
Increased turbidity can result from the construction of intake
structures in several ways. First, increased turbidity can result from
physical construction activities conducted below the water level of the
source. Such activities as dredging, pipe installation and backfilling,
and the installation and reiroval of coffer dams and related facilities
can create significant increases in turbidity unless these activities
are carefully controlled. The turbidity created by the physical
construction of intakes will normally be limited in duration to the
extent of the construction schedule. The impact of -his type of
turbidity increase on the source ecology is dependent upon the particle
size distribution of the sediment, the sediment transport
characteristics of the source, and the location of the important
organisms with respect to the intake construction activities.
There are a number of construction techniques that can be employed to
reduce the turbidity increases associated with these activities.
Excavation and dredging activities can be conducted behind embankments
or coffer dams to contain potential sediment discharges. Care must be
exercised to limit the turbidity increases due to the construction and
removal of these facilities. Onshore construction can be performed with
natural earth plugs left in place to prevent the discharge of material
to the source. Construction can be scheduled to take advantage of low
water periods and periods of reduced biological activity in the source.
Some sources will expose a large portion of the flood plain under low
water conditions allowing much of the intake structure to be constructed
in the dry area. Construction should also be scheduled around important
spawning periods, feeding periods and migrating periods to reduce impact
to these functions.
The control of dewatering activities can also be important. The
discharge of soil materials from dewatering activities can be limited by
the use of holding ponds or filtration equipment prior to discharge of
this water to the stream.
All material excavated or dredged in the construction of intakes should
be placed above the water line where possible. The laying of conduit
should be scheduled to minirrize the amount of time that the trench is
open. As soon as the conduit is placed, the trench should immediately
be backfilled and the surface of the trench smoothed over to prevent
errosion of the trench materials.
Long term turbidity increases can result from the entrainment of
material from spoil areas located either below the waterline or erosion
of material placed above the waterline. In addition, erosion of
126
-------
excavations and fills that are permanent parts of the intake can also
add turbidity that will persist long beyond the completion of
construction activities. Adequate stabilization of these fills may be
required which may necessitate rip-rap slope protection and seeding of
fill areas.
Disposal of Spoil
— j- - . — . -1
The disposal of spoil within navigable waters is controlled by the U.S.
Army ' Corps of Engineers. The disposal of spoil from excavation and
dredging activities can displace and destroy important benthic
organisms. The disposal of spoil in knowm fish spawning, nursery,
feeding areas, shellfish beds and over important benthic populations can
cause permanent loss of important biological species.
127
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SECTION V
OPERATION AND MAINTENANCE
Introduction
The environmentally related performance characteristics o± a cooling
water intake structure will be primarily established by the location and
design criteria discussed in the previous sections. While most adverse
environmental impact will result from the operation of the intake, rela-
tively little can be done by the application of appropriate operational
measures to significantly reduce such adverse environmental impact.
This results from the fact that during operation the intake is the
passive portion of the cooling water system, which simply supplies the
water demand of the plant. The only portions of the intake structure
that can be "operated" are the pumps and the screens. Only a small
degree of improvement of adverse environmental impact can be effectuated
by controls placed on these facilities.
The development of a continuing enforcement and performance monitoring
program might be of some value in determining desirable operating
conditions.
Maintenance is an aspect of intake structure operation which has direct
environmental impact. Good maintenance will require an effective
program of preventive maintenance for both above water and below water
portions of the intake.
Operation
Many conventional traveling screens are operated once during each eight
hour shift. During periods of high debris loading in the water source,
screens may be operated more frequently and in some cases continuously.
Pump operation is directly controlled by the water demand from the
plant. Little flexibility in the operation of either of these systems
is possible.
Screen Operation
The data available on screen operation suggest that, under certain
conditions, continuous operation of the screens can reduce impingement
effects. This is due to the fact that, with continuous screen
operation, fish are impinged for a shorter period of time. One of the
primary reasons for this is that fish typically tend to fight a
situation which they recognize as perilous such as being impinged on a
screen or being lifted out of water. The longer a fish is allowed to
fight such a situation, the more likely it is to damage itself.
129
-------
Continuous screen operation to reduce impingement effects is only
applicable where fish separation and bypass systems are available. The
number of installations having this capability is small. Continuous
screen operation will shorten screen life and increase maintenance costs
to some degree.
Pump Operation
Control of pump operation has been used at certain intakes (Plant No.
3608) in the northern latitudes to reduce impingement effects during the
winter months. This type of control involves the reduction of the
volume of water pumped during these cold water periods. Pump flows can
be reduced without detrimental effect on plant performance if water
temperatures are low enough to compensate for the reduced volume of
cooling water.
Since fish swimming ability for many species is drastically reduced at
low water temperatures, such a flow reduction in the winter period can
effectively reduce fish impingement. The best way to reduce water
intake volumes is to reduce the pump speed. This can only be done where
pumps have variable speed drives. Unfortunately, most circulating water
pumps do not have variable speed capability. Another way to reduce the
intake volume is to shut down a pump. This will cause increased
velocities through the remaining screens because of the pump runout
factors noted in the design section of this portion of the report.
On new structures the value of a reduced number of pumps operating in
winter should be evaluated and considered in the overall initial design.
Performance Monitoring
For several reasons, the development of a continuing performance
monitoring program in conjunction with the operation of intake
structures would be helpful. First, the data developed on the
performance of various intake systems under different regional
conditions could be used to develop a base on intake performance.
Second, it would allow the effectiveness of individual intaxe guidelines
to be determined and periodic updating of individual requirements where
desirable.
The following type of data would be included:
- source water temperatures
- Stream flows (where applicable)
- Screen operaton schedules
- Cooling water flow
- Number, types and condition of important organisms impinged,
entrained, and bypassed.
130
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Maintenance
An effective preventive maintenance program can be developed for both
below water and above water portions of the intake structure.
The maintenance of the above water portion of the intake will basically
consist of the maintenance cf the mechnical equipment associated with
the intake. This equipment includes primarily the screens and screen
drives, the trash racks and supporting equipment.
Suggested preventive maintenance procedures are normally supplied by the
manufacturer of the various systems. This program will consist of
regular lubrication schedules for all rccving parts and a firm inspection
program to check key wear points, particularly screen basket lugs,
headshaft lugs, carrying chains, etc. Inspection of the spray wash
system should also be made on a regular basis with particular emphasis
on the condition of the spray nozzles. The water screen should be
tested for binding and misalignment on a monthly basis by operating the
screen for several revolutions with the test shear pin left in place.
Adequate maintenance procedures also require the stocking of a spare
parts inventory because of long lead times which generally exist on
spare parts deliveries. The suggested list of spare parts will
generally be supplied by the equipment manufacturer.
Preventive maintenance of the portion of the intake below tne water line
is also important and also often neglected because it usually requires
the dewatering of the individual intake bays and/or use of divers.
Below water maintenance should include visual inspection of footwells
and footwell bushings on an annual basis. This may require a diver if
the well cannot be dewatered or the screen raised. In addition,
periodic below water inspection cf the intake can reveal the extent of
the following adverse conditions as noted in Reference 76:
Silt accumulation in front of the structures which can effect intake
hydraulics.
- Undermining of the base of the structure which might cause subsequent
collapse of the structure.
- Deterioration of stop log and screen guides.
Spalling concrete which may expose reinforcing bars and weaken the
structure.
- Damage to pump impeller and fittings which can lead to pump failure.
131
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SECTION VI
CCSI DATA
Introduction
This section contains cost data relative to cooling water intake
structures. The section is organized tc first present current costs for
the construction of the several types of conventional intake structures
commonly used by industrial establishments. This is done to establish a
baseline against which the additional costs associated with the
implementation of the control measures can be compared. Following the
development of this baseline cost data, estimates are made of the costs
associated with the certain intake structure control measures.
The cost data contained in this section are capital costs associated
with intake structure construction only. No consistent data on
operation and maintenance of cooling water intakes were available.
Records of these costs are not routinely kept by either the users or the
manufacturers of intake structure equipment. The magnitude of costs
associated with operation and maintenance of cooling water intake
structures are believed to be small.
A further qualification of the data contained in this section is
required. The scarcity of detailed data on the constructed cost of
intake structures was the major problem area in the development of this
document. This lack of data results from the fact that most intake
structures are constructed as part of a larger general contract which
includes other structures on the site, and in some cases, the complete
plant. It is difficult in these cases to separate the portion of the
costs that are directly associated with the intake structure either from
the bid package or from field records of the cost of construction put in
place. it was necessary therefore to synthesize the cost data available
from several sources. In doing this, the costs of intakes constructed
at ditferent dates and in different geographical areas of the country
arp combined without normalization of the data with respect to either
inflationary factors in the construction market or well established
regional cost differences. The cost data presented must therefore be
considered to be order of magnitude costs and should be used in this
context only.
Cost of Construction of Conventional Intake Structures
The cost of conventional intake structures is influenced by both the
type of intake and the size of the intake facility. The cost of the
major piece of mechanical equipment in the intake, the traveling water
screen, contributes a relatively small portion of the total intake
structure cost.
133
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Screen Costs
The costs of furnishing and installing intake water screens are readily
available from any of the leading screen manufacturers. Table Vl-1 is a
tabulation of the cost of 16 conventional traveling water screen
installations provided by a leading screen manufacturer during 1971.
These costs have been converted to a unit flow basis and the results
tabulated in the next to the last column of the table. The approach
velocity for each installation is recorded in the last column. The
factors that most effect the cost of the screens are tne approach
velocity and the size of the plant. The total range of screen cost was
from $2,000/m3/s ($0.13/gpm) to $37,40Q/m3/s ($2.36/gpm) . The effect of
approach velocity was pronounced with the average unit cost for
installations where approach velocity exceeded 0.3 m/s (1 fps) being
$5,200/m3/s ($0.33/gpm) compared to a cost of $16,600/m3/s (*1.05/gpm)
for installations where the approach velocity was less than 0.3 m/s (1
fps). The variation with the size of flow was even more significant.
The cost of large screening units (greater than 6.3 m3/s (100,000 gpm)
per screen averaged $3,200/m3/s ($0.20/gpm) as compared to #17,400/m3/s
($1.10/gpm) for smaller units (less than 3.2 m3/s (50,000 gpm) per
screen.
Intake Structure Costs
Estimated cost data for the three different types of intake structures
are shown in Figure VI-1. These data were taken from Reference 11 for
small powerplants and from estimated costs of individual large plants
from various sources. The base year fcr these cost data is 1971. The
figure demonstrates the two important cost impacting factors in
conventional intake construction. The first of these is the type of
intake used. The offshore intake will ccst significantly more in all
size ranges than either the shoreline intake or the channel type. The
basic reason for this is the cost of excavation and laying of offshore
conduit. The cost differences between the channel type of intake and
the shoreline intake appear to be small except in the lower size ranges.
The other significant cost factor is the size of the plant. The cost of
construction of all three types of intakes are shown to be significantly
higher for smaller plant sizes than for larger powerplants. For
instance, the costs of offshore intakes are shown in Figure VI-1 to vary
from as low as $3/KW of installed electrical generating capacity for a
1000-MW plant to as high as $90/KW for plants under 10 MW.
The data contained in the Figure have been standardized on the basis of
significant cost factors. The length of pipe used in the development of
the curve for offshore intakes was 975 M (3200 ft). Likewise, a
constant 127,700 m3 (167,000 cu yds) of excavation was assumed for all
channel intakes. The amount of these items and their costs can vary
significantly. Reference 24 shows the costs of three offshore intakes
constructed between 1955 and 1958. The cost of installation of the
134
-------
Ln
TABLE VI-1
COST OF TRAVELING WATER SCREENS (1971)
Plant
Code
No.
4709
1243
4817
N.A.
4001
4829
N.A.
2110
1003
1731
1002
0616
0108
0109
N.A.
N.A.
Number
of TWS
6
1
4
6
4
3
2
1
8
3
2
1
3
2
6
1
Basket
Size
(m)
4.
1.
2.
3.
3.
3.
1.
3.
3.
3.
3.
3.
2.
2.
3.
1.
27
52
13
05
05
05
52
05
05
05
05
05
44
74
05
78
Centers
(m)
17.98
7.01
9.75
11.58
10.58
13.72
5.18
31.39
10.97
11.89
6.40
9.45
19.81
10.06
8.84
11.58
Type Flow Design Low
of per TWS Water Depth
Water m-^/s m
Fresh
Fresh
Salt or
Brackish
Fresh
Fresh
Salt
Salt
Fresh
Fresh
Fresh
Brackish
Salt
Fresh
Fresh
Salt
Salt
11.91
.94
4.50
7.91
5.36
8.14
1.03
4.72
3.20
8.63
2.90
6.93
2.19
0.69
1.73
1.26
8
1
5
6
5
6
2
5
6
8
3
4
5
4
3
2
.53
.68
.18
.70
.49
.25
.74
.79
.19
.53
.05
.11
.33
.72
.35
.40
Frame Approx .
(No Posts) Cost
$
4
2
4
2
2
2
4
4
2
2
2
2
4
2
2
2
228,
16,
120,
144,
84,
87,
33,
49,
197,
53,
30,
29,
93,
52,
137,
23,
000
000
000
000
000
000
000
000
000
00
000
000
000
000
000
000
Unit
Cost
$/m3/s
3,200
17,000
6,700
3,000
3,900
3,600
16,000
10,400
7,700
2,000
5,200
4,200
14,200
37,400
13,200
18,300
Velocity
m/s
0.326
0.369
0.409
0.387
0.320
0.427
0.244
0.268
0.171
0.332
0.305
0.549
0.168
0.052
0.168
0.290
-------
100
o
u
t/)
(0
-p
Offshore Intake 975 m long
Channel Intake 127,700 m3 dredged
Off SHOlZt lU7AVi6r
100 200 300 400 500 600 700 800 900 1000
Size (MW)
COST OF INTAKE SYSTEMS
FIGURE VI-1
136
-------
offshore piping for these powerplants varied from as low as $2.16 to
$4.70 per KW installed. Caution is therefore suggested in the use of
this figure. Costs of each type of intake can vary considerably from
the curves shown.
Additional data on the cost of shoreline intakes are contained in Table
VI-2. The Table contains cost data on five cooling water intake
structures and four makeup water intake structures constructed after
1965. With the exception of three makeup water structures the cost data
contained in the table represenr constructicn actually put in place.
The costs of the three makeup water intakes are detailed cost estimates
since these plants are now still under construction. Tne cost data
contained in rhe table are substantially the same as in Figure VI-1.
The cost of shoreline intakes runs from between $l-$4/KW ±or the larger
size powerplants. The cost differences between makeup water systems and
circulation water systems does not appear, from the Table, to be as
great on a $/KW basis as the difference in intake flow volume would
indicate. The cost data, on a flow basis, appear to range from $40 to
$90 per gpm of flow for makeup water intakes and from $6 to $30 per gpm
of flow for circulating water intakes. For both these types of systems
the upper cost ranges are for nuclear powerplants. The nuclear service
intakes, although pumping much smaller volumes of water, are becoming as
large as the circulating water intakes in order to accomodate backup
equipment, provide missile protection and insure operation under maximum
probable storm, water flood and drawdown levels. The data presented in
Table VI-2 can be compared to the screen cost data on the basis of
$/m3/s ($/gpm). It can be seen that the cost of the screens is a
relatively small portion (less 1-2%) of the intake structure cost. The
bulk of the cost of intakes are associated structural features, and are
relatively independent of equipment costs, at least for conventional
intakes.
Typical rule of thumb estimating guides for intakes are the following:
Water screens cost approximately $ll/m2 ($1.00/ft2) of
screen surface with a range of $5.50 to $24.22/m2
($.50 to $2.25/ft2) .
- The cost of construction of offshore pipeline can vary
from as low as $500/m ($150/ft) for small makeup water
lines to as much as $6,600/m ($2,000/ft) for large maxeup
water lines.
The cost of shoreline intakes will average approximately
$ll,000/m2 ($l,000/ft2 27i based on the cross-sectional
area of the screens.
Shoreline intakes will also vary from between $140 to
$424/m3 ($4 to $12/cu ft) of structure enclosed beneatn
the operating deck with a mean of $212/m3 ($6/ft3).
137
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TABLE VI-2
COST OF INTAKE STRUCTURES
CD
Plant
Code
No.
5404
5309
4213
3407A
3407
3805
Unit 1
3805
Unit 2
3601A
3113
Intake
Flow
m3/s
1.26
1.58
1.58
2.27
20.79
4.85
5.67
20.79
20.16
Total
Cost
$
466,000
2,000,000
2,500,000
5,000,000
1,000,000
400,000
950,000
4,800,000
8,700,000
Unit
Cost
$/m3/s
369,800
1,265,800
1,582,300
2,202,600
48,100
82,500
167,500
230,900
431,500
Unit
Cost
$/kw
0.40
1.82
1.37
4.17
1.78
1.67
2.26
4.00
11.18
i
Plant
Fuel
Fossil
Nuclear
Nuclear
Nuclear
Nuclear
Fossil
Fossil
Fossil
Nuclear
Comments
Intake
Type
Makeup
Makeup
Makeup
Makeup
Year
Commissioned
Circulating
Water
Circulating
Water
Circulating
Water
Circulating
Water
Circulating
1965
1976
1975
1977
1965
1966
1973
1972
1972
Water
-------
PrQBQged_Gu_idelines
Locational Measures
The measures which potentially have the greatest cost: impact on intake
structures are concerned with the location of the intake. In
particular, where locational measures involve extensive offshore piping
at a site for which a shoreline intake would have otnerwise been
suitable, the intake cost can be increased significantly. Costs of
offshore piping have been detailed above, and it was snown that the cost
of this work can increase the intake cost significantly.
Design Measures
The design measures that will increase costs significantly are those
that involve a reduced approach velocity and flush mounting of the
screens. The changes that could be involved are shown in Figures VI-2
and VI-3. These figures are based on a certain design of a hypothetical
shoreline intake* structure without the modifications required. The
unmodified design provides an approach velocity of 0.6/m/s (2 fps) with
screens set back from the front face of the intake. The modified design
amploys an approach velocity of 0.15 m/s (0.5 fps) with screens set at
the front of the intake and fish passageways provided berween the
screens and the trash racks. The total intake xlow-per-bay is
approximately 10.1 m3/s (160,000 gpm) at maximum pump runout conditions.
The intake would draw an average of 15.8 m3/s (250,000 gpm) using two
bays with the third bay acting as a spare. This flow is equivalent to
the circulating water flow for a fossil-fired plant with a capacity of
approximately 300 MW.
The major changes involved include the increasing of the volume of the
intake structure below the operating floor from approximately 1190
m3 (42,000 ft3) as shown in Figure VI-2 to approximately 2040 m3 (72,000
ft3) as shown in Figure VI-3. The cost increase involved in making
these changes are shown in Table VI-3.
TABLE VI-3
COST ANALYSIS - IMPLEMENTATION OF EXAMPLE DESIGN REQUIREMENTS
Unmodified Intake Modified Intake
Facility Cost Cost
Structure $ 189,000 $ 324,000
Racks 17,000 38,000
Traveling Screens 54,000 80,000
TOTAL J 260,000 $ 442,000
139
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17.5m (581)
Screens
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PLAN
Pumps
ELEVATION
U1
3
KJ
Ul
Total Flow
60m3/S
(160,000 gpm)
Approximate Volume
below the operating
floor: 1189 m3
(42,000 cubic feet)
DESIGN OF CONVENTIONAL INTAKE
FIGURE VI-2
140
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18m (60V
•>
T, W V
0.15mps ——
(0.5 fps)
a
rn mm
1
n,
O
s:
1111
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NJ
t.
|ro
loo
I
O
-J
LH
3
to
Ul
r^a
Shoreline (sheet pile waterfront wall)
PLAN
Total Flow
[-) 9m(3C
-. .». ./Lf
+ 3.2m (10.5';
3
(160,000 gpm)
n
<->n
3m (20 ')
Approximate Volume
below the operating
floor: 2040m3
(72,000 cubic feet)
ELEVATION
DESIGN OF CONVENTIONAL INTAKE MODIFIED BY RECOMMENDATIONS
FIGURE VI-3
141
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The total cost increase involved in making these changes is shown in the
Table to be approximately $182,000 or roughly 70% of the cost of the
unmodified intake.
In addition, the larger structure requires more dredging and the
construction of a sheet pile retaining wall upstream and downstream of
the intake to provide continuity to the "flush-face" intake, and to
facilitate flow through the fish passage between the trash rack and
traveling screens. The estimated cost for the additional work (dredging
and retaining wall) is $90,000.
The estimated cost of modifying the traveling water screens to
incorporate fish handling and bypass systems as discussed in the design
section of this portion of the report is between $15,000 and i20,000 per
bay depending on the screen size. An equivalent amount could be
required to provide the additional screen wash systems and bypass
systems required.
Costs - Other Measures
There will be additional costs for measures related to construction and
performance monitoring. The costs of these measures are indeterminable
at this time, but are not believed to be excessive.
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SECTION VII
CONCLUSIONS AND RECOMMENDED TECHNOLOGY
TO BE CONSIDERED IN EACH CASE
Introduction
This section summarizes the findings of the previous sections on
background, location, design, construction and operation and maintenance
of cooling water intake structures. The format for -this section
presents certain conclusions with respect to the various factors
involved. The technology dicussed herein were prepared to assist in the
evaluation of the best technology available for minimizing environmental
impacts of cooling water intake structures. As a minimum, the following
recommended technology should be considered in each case.
Background
It was concluded that the application of the best technology available
on intake structures alone will do little to protect against the
entrainment effects on small organisms passing through a cooling system.
These effects are better controlled ty either controlling the plant
intake flow or the design of the cooling water systems. Such measures
do not relate to cooling water intakes per se, and therefore are beyond
the scope of this report.
It was found that some intakes have been designed without the
development of adequate data on the biological community that would be
affected by intake operation. Since subsequent measures for location,
design and construction can only be made on the basis of this
information, this data base should be developed in each case.
Technology - Acquisition of Biological Data
The discharger should provide data on the biological community to be
protected. In some cases, depending on the severity of the problems and
especially for new steam electric powerplants withdrawing water from
sensitive water bodies, the data should consist of, as a minimum, the
following:
- The identification of the major aquatic species in the water
source. This should include estimates of population densi-
ties for each species identified, preferably over several
generations to account for variations that may occur.
- The temporal and spatial distribution of the identified
species with particular emphasis on the location of spawn-
143
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grounds, migratory passageways, nursery areas, shellfish
beds, etc.
- Data on source water temperatures for the full year.
- Documentation of fish swimming capabilities for the species
identified, and the temperature range anticipated under test
conditions that simulate as close as possible the conditions
that exist at the intake.
- Location of the intake with respect to the seasonal and diurnal spatial
diurnal spatial distribution cf the identified aquatic species.
Location
The proper location of the intake structure with respect to the aquatic
environment is far and away the most important consideration relevant to
applying the best technology available for cooling water intakes. Care
in the location of the intake can act to grossly minimize adverse
environmental impacts. It will be difficult and perhaps impossible in
certain cases to offset the adverse environmental impact of improper
intake location by subsequent changes in either design or operation of
the intake structure short of significantly reducing the intake volume.
Therefore, it is critical that the qualifications of the biological and
other investigators and the data obtained, especially as a preliminary
to the location of a new intake, reflect the significance of the
decisions which must rely on the results of the study.
Intake Location With Respect to Plant Circulation Water Discharge
The potentially adverse effects of the recirculation of water from the
discharge back to the intake have been discussed. Most powerplants will
prevent this to maximize plant thermal efficiency. In some cases where
this is difficult to do, some recirculation may be tolerated. From the
environmental standpoint, recirculaticn of warm water is undesirable.
Technology - Prevention of Warm Water Recirculation
All intakes should be located with respect to the plant, discharges in a
manner that will prevent, to as great an extent as possible, the
recirculation of warm water from the discharge back to the intake.
Plant and Vertical Location of the Water Inlet
The location of the water inlet with respect to the temporal and spatial
distribution of the resident and migratory aquatic populations is
extremely important. Intake configuration can be selected to withdraw
144
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water from any point in the source water body. Inlets can be located to
draft water from any elevation in the source.
Technology - Location and Elevation of Water Inlet
Water inlets should be designed to withdraw water from zones of the
source that are the least productive biologically and contain the lowest
population densities of the critical aquatic organisms. This includes
both the plan and location of the inlet and the vertical location in the
source water body.
In addition, inlets should be located to avoid spawning areas, nursery
areas, fish migration paths, shellfish beds or any location where field
investigations have revealed a high concentration of aquatic life.
The location of the intake should alsc be selected to take advantage of
river or tidal currents which can assist in carrying aquatic life past
the inlet area or past the face of the screens.
Intake Location With Respect tc the Plant
The incremental impact on entrained organisms is directly related to the
transit time between the intake and the condenser. However, all
entrained organisms would be lost, anyway, in configured recirculating
cooling water systems. Therefore, for other types of cooling water
systems the intake should be located close to the plant. This
consideration is even more important in the relative location of the
outfall structure and the plant.
Technology - Location of Intake With Respect to the Plant
For nonrecirculating cooling water systems the intake structure should
be located close to the plant.
The basic conclusion related to the design section is that there is no
generally viable alternative to the conventional traveling water screen
available at the present time. Some new screen types have recently been
developed that might prove to have generally superior environmental
characteristics following an adequate period of testing. Certain of
these designs might be superior today at certain sites. It is noted
that this is one area in which research and development have not kept
pace with the need. Research projects directed toward the development
of more effective screening systems could have valuable results.
Furthermore, since the configuration of the intake is largely determined
by the screening system employed, the conventional intake structure will
probably remain substantially unchanged in the near future.
145
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Therefore, most of the design recommendations contained herein are based
on the configuration and physical design features of conventional intake
structures as previously defined in Section III. It is anticipated that
new^intake designs will emerge that may have more positive environmental
design features than the conventional intake. One of the express
overall recommendations is the encouragement of this positive
evolutionary process in the technology. As dicussed in Section III,
some of the new technologies that will influence intake design have
already been partially explored. These include the increased use of
behavorial barriers such as the louvered intakes; the development of new
types of physical screening systems such as the horizontal travelling
screen; and the increased use of bypass systems. The present status of
these technologies and their very limited use at existing cooling water
intake structures does not justify separate recommendations for these
types of systems at the present time. However, certain features of the
following recommendations may be applicable to these types of systems,
as well as to conventional intake structures.
Approach Velocities
Typical approach velocities to the traveling water screens at existing
intakes fall within the range cf about 0.24 to 0.33 mps (0.8 to 1.1
f ps) .
Technology - Design Approach Velocities
The design approach velocity to the intake water screens should be
measured in the screen channel upstream from the screens and be based on
the effective portion of the screen face. The velocity measurement
should further be based on the lowest water level anticipated. The
design approach velocity should be conservatively based on data specific
to the design organism(s) at the intake location. These data should
include as a minimum:
- The spatial and temporal distribution of the fish by size
for each species identified.
- The annual temperature range anticipated at the intake.
- The demonstrated avoidance capability of these species over
the full range of temperatures experienced.
It is possible that a low approach velocity could have a more
adverse environmental impact than a higher approach velocity.
Uniform Approach Velocities and Effective Screen Areas
The maintenance of uniform velocity profiles across the screen face is
an important feature in effective screen performance. Many factors can
influence the velocity gradient at the screen face and it is not a
146
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simple task to eliminate non-uniform velocities. Another important
consideration is the determination of the effective area to be used in
determining the approach velocity. In many cases, the effective area is
significantly less than the full submerged area of the screen.
Technology - Uniform Approach Velocities
The discharger should document that effectively uniform velocities will
be maintained across the face of the screen at the design conditions.
The discharger should also indicate the effective screen area used in
the approach velocity calculation. Where there is reason to question
this information, hydraulic model testing, as well as velocity profile
measurements taken at the intake should te required of the applicant.
selection of Screen Mesh Size
The selection of screen mesh size is generally based on providing a
clear opening of no more than one-half of the inside diameter of the
condenser tubes. The powerplant industry has generally standardized on
0.95cm(3/8") mesh size. While this criteron may be adequate for keeping
foreign objects out of the cooling system, this criteria may not be
adequate for proper proection of all aquatic species. A rational design
approach for screen mesh selection based on the design organism(s) is
contained in the design portion of the report. The data used in this
approach are not considered extensive enough for development of a firm
recommendation on screen mesh size.
However, this approach may be used in lieu of better data. More
information on this aspect of screen design should become available in
the future as the biological data required above are developed.
Behavorial Screening Systems
None of the available behavorial screening systems have demonstrated
consistently high efficiencies in diverting fish away from powerplant or
other industrial intake structures. The behavorial screening systems
based on velocity change appear to be adequately demonstrated for
particular locations and species, at least on an experimental basis.
More data on the performance of large prototype systems at industrial
plants will be required before the louver system can be recommended for
a broad class of intakes. The "velocity cap" intake can be recommended
to be considered for all offshore vertical intakes since it would add
relatively little to the cost of the intake, and has been shown to be
generally effective in reducing fish intake to these systems.
The performance of the electric screening systems and the air bubble
curtain appears to be quite erratic, and the mechanisms governing their
application are not fully understood at the present. Tnese types of
systems might be experimented with in an attempt to solve localized
147
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problems at existing intakes, since the costs involved in installing
these systems are relatively small.
No successful application of light or sound barriers has been
identified. It appears that fish become accustomed to tnese stimuli,
thus making these barriers the least practical of the available
behavorial systems on the basis of current technology.
Technology - "Velocity Cap" Intakes
All offshore intakes should be fitted with a "velocity cap" designed to
minimize the intake of the design organism (s) that are resident at the
individual intake location. The design approach velocity measured at
the face of the intake opening should conform to the design approach
velocities previously discussed.
Physical Screening Systems
It is concluded that the conventional traveling water screen will
continue to be widely used at powerplants for the near term, although
this system may have some potentially significant adverse environmental
features.
Furthermore, the fixed screening systems currently installed at
powerplant intakes, have potentially even more damaging environmental
characteristics. These systems invariably involve longer impingement
periods between cleaning cycles and increased damage to the fish because
of greater local velocities across the more completely clogged screen.
The crude methods employed to clean fixed screens are also damaging to
fish.
Technology - Limitation of the Use of Fixed Screens
The use of fixed or stationary screening systems should be prohibited at
powerplant intakes. The cost impact of this would be relatively small,
since the higher initial cost of rotating equipment will be offset by
the reduced labor required for manual cleaning of the screens over the
lifetime of the intake.
Fish Handling and Bypass Facilities
There is some evidence to recommend that all new intakes should
incorporate a fish handling and bypass system which will allow for safe
return of important fish species to the water source along with the
physical screening system. Unfortunately, the case of fish handling and
bypass systems in conjunction with cooling water intakes is not a highly
developed technology at the present time. Therefore, a blanket
recommendation, requiring these systems at all new intakes cannot be
recommended, but this technology should be considered in such case.
148
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The use of fish bypass facilities at existing intakes where fish
impingement has been documented may improve the performance of these
intakes. These types of facilities may also be desirable in those new
intakes where it is not clear that impingement can be avoided. One type
of bypass system can be incorporated in the conventional intake using
the traveling water screen. This system assumes impingement but
minimizes its effect in the following manner:
- Impingement time is reduced by continuous operation or rhe
screens
- It provides a means for a gentle separation of the fish
from the screen mesh
- It provides a passageway for safe return of fish to the water
way
One installation of this type is presently being installed on a major
powerplant intake (Plant No. 5111) and was described in detail in the
design section of this report. The basic features of this system are
shown in Figure III-U1. It is believed that this type of system might
have a positive impact on the impingement problem if the performance of
this initial installation is successful. However, this system is not
sufficiently developed at present to provide a basis tor a formal
general recommendation. The progress of this type of facility should be
closely followed in the future because the system appears to have
attractive environmental features.
Control of Fouling and Corrosion
Biological fouling of the cooling water system downstream of the intake
is usually controlled by the addition of chlorine to the cooling water.
The point of application is often the intake structure. The application
of chlorine at the intake can adversely affect any subsequent fish
bypass system that may be installed. It is, therefore, important that
if chlorine is to be administered at the intake it should be added
downstream of any such facility. It is noted that the addition of
chlorine at this point will seriously affect the survival chances of all
entrained organisms, and its use should be carefully monitored and
controlled.
Corrosion protection of the screening system is not a design factor of
intakes that directly affects the environment. It will be to the
advantage of the owner to insure the integrity of screening systems by
providing adequate materials for the type of use and water quality of
the source.
149
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Intake Configuration
Of the three conventional intake structure types discussed in the design
section of this report, the approach channel type of intake generally
has sufficient potential for environmental impact to warrant careful
evaluation prior to its use. This type of intake is shown in Figure
111-47.
Technology - Use of Approach Channel Intakes
The use of lengthy approach channel intakes should be avoided where at
all possible. Where they are used, the screening facility should be
located as close as possible to the shoreline while maintaining a
satisfactorily uniform velocity distribution. An arrangement is shown
in Figure 111-48. The velocity in the approach channel should be
limited to the design approach velocity.
There are further considerations in the design of a shoreline intake.
In some cases at nuclear powerplants, it may not practical, for safety
reasons, to locate the screen structure or intake on the shoreline.
Also, the placement of the intake with respect to the shoreline, should
be such as to limit the protrusion of the intake into the stream, except
in the case of an ocean site. Protuding intakes cause localized eddy
currents that can affect the travel of fish to the intake. An example
of this type of design is shown in Figure 111-49.
Technology - Limitation of Protruding Shoreline Intakes
Intakes should be designed to limit the protrusion of the intake
sidewalls in the stream.
Another important design consideration for shoreline intakes is the
location of the screens within the confining sidewalls of the intake.
Most conventional intakes have the screens set back from the face of the
intake between confining sidewalls. This type of setting can create
undesirable entrapment zones between the trash racks and the screens.
The recommended setting is to mount the screens flush with the front
face of the intake as shown in Figure 111-50. In this type of design,
it is also desirable to design the trash racks to allow fish passage in
front of the screens. This type of intake is most suited to locations
where there is sufficient current in the source to wash the fish past
the intake. Two examples of this type of design incorporated in
existing powerplants are shown in Figures 111-51 (Plant No. 3601) and
111-52 (Plant No. 0610).
Technology - Screen Settings for Shoreline Intakes
The screen settings for all shoreline intakes should provide for
mounting the screens flush with the upstream face of the intake. In
addition, provisions should be made for fish passageways located between
the screens and the trash racks.
150
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Use of Walls
Walls are often used to select water from the coldest portion of the
source. The use of a wall is shown in Figure III-4. Walls not only
create non-uniform velocity conditions at the screens, but also create a
dead area where fish can become entrapped. Fish will nor usually swim
back under the wall to safety. It is recommended that this type of
construction be avoided.
Technology - Limitation on the Use of Walls
The use of walls for the purpose of selecting ccld water should be
avoided. Walls may be used where required to prevent the recirculation
of warm water or to select water from biologically safe areas of the
source. Both of these factors are contained in previous guidelines.
Pier Design
Many intakes utilize a pier which protrudes upstream of the screens and
serves as a dividing wall between adjacent screen channels. This type
of design is shown in Figure 111-53, and is not consistent with the
concept of flush mounting of screens and should therefore not be used.
Pump ;to Screen Relationships
The relationship of the pump capacity to the screen area provided is an
important design factor at intake structures. Several intake variations
to accomodate pumps of a wide range of sizes is shown in Figure 111-56.
Care must be taken to locate the screen with respect to the pump in a
manner which will properly utilize the entire screen surface. Any mis-
match between screen size and pump size can result in undesirable
velocity distribution across the screen. Hydraulic Institute Standards
recommend minimum distances from screen to pump as well as lateral
dimensions of the screen and pump wells. However, these recommendations
are based on pump performance criteria and not best utilization of the
screen area.
Another important design consideration is the effect on screen
velocities under pump run-out conditions. This condition exists where
one pump is removed from service and the total dynamic head on the
remaining pumps is reduced. Flow through the remaining screens may be
increased by as much as U0% above average design conditions.
It is impossible to establish a uniform recommendation that would re-
flect the different problems that might arise because of the several
pump-screen relationships that exist. However, dischargers should be
required to show how their designs have allowed for these factors.
151
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Ice Control Facilities
Most intakes located in the northern latitudes employ a partial
recirculation of warm condenser discharge back to the intake to control
ice buildup in front of the intake. The potential adverse environmental
effects of warm water recirculation have been well documented. Fish
will be attracted to the intake in the winter months. At tne low water
temperatures their swimming capability will be greatly reduced and the
possibility of their entrapment in the intake will be increased.
Unfortunately, there is no alternate ice control technology currently
available to replace hot water recirculation. Submerging the intakes
can create another problem as noted in an earlier section. Air bubble
systems have not been proven on large cooling water intakes, although
they may becoma acceptable following a further period of development.
The development of alternate technology for the control of ice at intake
structures is one area in which further research should be undertaken.
However, until such technology is available the use of hot water
recirculation cannot be prohibited. These systems perform an important
function at intake structures. For this reason, the recommendation for
ice control must be qualified in a manner that does not prohibit this
system but encourages the development of alternate technology.
Technology - Ice Control at Intakes
The use of warm water recirculation for the purposes of controlling ice
at intake structures should be limited to those installations where no
other means of ice control are available. Where such a system is
employed, close control of the quantity of water recirculated and timing
of its use (intermittent if possible) should be practiced. The point of
application of the hot water should be located to minimize the potential
adverse environmental impact that can result from the application of
these systems. The applicant is encouraged to seek alternate solutions
to the ice control problem. Intermittent operation of ice control could
prevent fish accumulations which might occur with a continuous ice
control.
Aesthetic Design
Where the intake structure and the balance of the plant are separated by
great distances, the intake structure can have an objectionable physical
presence. This will be significant in wilderness areas and in natural
and historic preserves. There are various techniques available to blend
the intake structure with its surroundings. The intake may also be
lowered to reduce its impact. However, this latter approach can
increase costs significantly especially where rock excavation is
required. Where the plant and intake are located close together, the
intake will be dominated by the plant and various architectural
treatments can be applied to create an attractive grouping of
structures. This latter factor is another reason for locating intakes
close to the balance of the plant. Since aesthetic impacts are governed
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by location conditions, a general measure for aesthetic design is not
recommended.
Noise control
The sound level of large circulating water pumps can be quite high.
Again this will be important only where the intake is remotely located
from the balance of the plant. The noise level emanating from an intake
located close to the plant will be dominated by the noise o± the plant.
Current practice, however, is to construct intakes, in milder climates,
without enclosures. Where intake noise level is a factor, they should
be enclosed. Enclosed intakes would not have significant sound levels.
A uniform measure is not recommended.
Construction
The adverse environmental impact of the construction of cooling water
intake structures consists almost entirely of the effects of the aquatic
population of the turbidity increases created £>y the various
construction activities. The U.S. Army Corps of Engineers already is
responsible for construction in navigable waterways and all intake
construction will have to conform to the corps' guidelines for dredging,
disposal of soil, etc.
Dredging, Excavation and Backfilling
These activities can cause significant short term increases in the
turbidity of the source water. Depending on the particle size,
distribution of the excavated materials and the hydrology of the source,
the impact of the turbidity increase will be local or widespread. It is
believed that a two-fold approach for the control of turbidity increase
is required. First an absolute limit should be placed on tne level of
turbidity increase resulting from these operations. Second, typical
requirements, as follows, should be utilized to reduce the impact of
individual construction operations.
Technology - Turbidity Increase Resulting From Dredging Excavation and
Backfilling
The turbidity increase from construction operations on cooling water
intake structures should not exceed a specific level of Jackson
turbidity units (JTU) set for the particular site. The method and
location of the point of measurement should depend on the nature of the
aquatic community, the length of the construction program and the
hydrology of the receiving water. This acceptable level of turbidity
should be based, as a minimum, on existing water quality standards for
the classification of the particular water body.
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Technology - Typical Requirements for Dredging, Excavation and
Backfilling
- Excavation in low lying areas in the vicinity of the water
body should be conducted with natural soil plugs or berms
left in place. When these soil plugs are removed, the one
furthest away from the stream should te removed first.
- Where excavations are dewatered during construction, no
discharge from the dewatering pump should be made to the
waterbody unless it conforms to the turbidity standard set
forth above; this may be require that the said discharges be
settled or filtered prior to discharge.
- Materials excavated should be placed above the water line.
Suitable slope protection for excavated materials should be
provided.
- Underwater excavations for conduit should be scheduled to allow
placing of the conduit and the closing of the excavation to be
completed as rapidly as possible. Backfill over conduit below
the water line should be leveled to prevent sediment transport.
- Where large excavations and dredging operations are required
it may be desirable to conduct these operations behind a re-
taining structure such as an earth embankment or a coffer dam.
Care must be taken in the construction and removal of these
facilities so that the turbidity limits established above are
not exceeded.
The applicable outline specifications contained above should be
incorporated in all intake construction where required. The discharger
should indicate that these specifications shall be incorporated into the
contract documents for the construction of the intake.
Construction Scheduling
The construction of intakes can often be scheduled in a manner that can
reduce adverse environmental impact. In many waterbodies there are
significant water level variations during the year. It may be possible
to schedule much of the intake construction during low wat^r periods
when it can be done above water level. In addition, construction should
be scheduled to avoid spawning seasons and migration periods where
turbidity increase can harm these functions. The ability to schedule in
this fashion requires that the appropriate biological data be made
available.
Technology - Construction Scheduling
The scheduling of intake structure construction should take advantage of
low water periods to undertake certain construction work above the water
level. Scheduling should also avoid kncwn periods of fish spawning and
migration.
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Disposal of Spoil
The disposal of spoil within navigable waters is controlled by the U.S.
Army Corps of Engineers. In addition to any requirements that the Corps
establish, it is necessary to prevent the disposal of spoil in known
fish spawning, feeding areas, shellfish beds and over important benthic
deposits. The disposal of spoil in these areas can cause permanent loss
of important biological species. In addition, spoil deposits both below
the water and above the water should be adequately stabilized to prevent
long term turbidity increases due to either water currents or erosion.
Technology - Disposal of Spoil
The disposal of spoil below the water line should be avoided. In those
cases where this cannot be avoided, spoil should not be disposed of in
spawning grounds, feeding areas and over important bentnic deposits.
All spoil deposits should be adequately stabilized to prevent long term
ero si on.
Slope Protection for Excavation and Fills
The same considerations governing the stabilization of spoil deposits
are also applicable to the protection of slopes of excavation and fills
that are a permanent part of the intake.
Technology - Slope Protection for Intake Excavations and Fills
The slopes of all excavations and fills incorporated in the intake
structure shall be adequately protected against erosion and wave action.
Operation and^Maintenance
Although most of the environmental impact may occur during actual intake
operation, it will not be possible to effect intake operation
significantly once it is placed in service.
Most of the control of adverse environmental impact of intake structures
would probably be obtained in the location and design criteria. Some
degree of control over impingement effects might be achieved by proper
screen operational procedures. Pump operation might also be controlled
to reduce environmental impact although the pumps are not a part of the
intake structure as strictly definad. It would also be desirable to
develop a program for periodic performance monitoring of intake
structures.
Maintenance is not an aspect of intake structure operation which has
only indirect environmental impact. The discharger should submit in
outline form his maintenance program for the intake system.
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Screen Operation
The impact of fish impingement on screens can be reduced by continuous
screen operation to reduce the period of time that fish are impinged on
the screens. This type of operation to reduce impingement effects
is only applicable_ where fish separation and bypass streams are_
available. Since the number of installations having this capability is
small, no general recommendations or continuous screen operation are
made. However, more of these systems may be installed in the future.
Continuous screen operation in this manner will shorten screen life and
increase maintenance costs.
Pump Operation
The ability to control pump operation can reduce impingement effects at
certain locations during the winter months. Pump flows often can be
reduced in the colder winter months with no detrimental effect on plant
performance. Since fish swimming ability is reduced during colder
temperatures, such a flow reduction may be desirable to reduce fish
impingement. Since the pumps are not a part of the intake as previously
defined, no measures regarding pump performance are recommended.
However, pump controls may be desirable in certain locations.
Performance Monitoring
A program of performance monitoring of intakes is recommended to
establish data on the performance of these systems.
Technology - Performance Monitoring of Intake Structures
The performance of intakes should be monitored on a continuing basis.
The owners of intake structures should periodically submit performance
data that consisting of the following:
- Source water temperatures
- Stream flows (if applicable)
- Screen operation schedule
- Cooling water flow
- Number, types, and condition of important organisms
impinged, entrained, and bypassed.
Applicability of Intake Structure Technology
For new sources, no measure other than proper location of the intake in
correspondence iwth the intake volumes required should be relied upon.
In many cases an existing establishment may have reason to replace the
nonrecirculating cooling water system with an essentially closed
recirculating system. The reduction in intake water quantity by
installing the closed cooling system should significantly reduce adverse
environmental impact resulting from the cooling para like water intake.
156
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Furthermore, intake flow could be reduced during certain time periods to
minimize adverse environmental impact.
A stepwise approach to intake modifications is generally recommended for
cases where adverse environmental impact must be reduced by this means:
The first step should be to attempt to reduce impact by the
modifications of the existing screening systems. The possible
modifications that can be applied are discussed in the design section of
this report. The performance of this type of modification has not been
fully documented because initial installation is presently under
construction. However, the cost of in-place modifications of this type
are not excessive and they can generally be made while the plant is
operating.
The second step should be to increase the size of the intake to reduce
high approach velocities. This will require additional screen and pump
bays and most likely the replacement of the existing pumps to reduce the
flow through each bay. This type of modification could also be done
while the structure is kept in service but only where extra screen bays
are available.
The third step should be to abandon the existing intake and replace it
with a new intake at a different location and incorporting an
appropriate design. This could be very costly particularly if an
offshore inlet is required. The recommendation of such a change should
be very carefully considered. However, a particular discharger may
elect to avoid the costs and uncertainties associated with the fixst two
steps and proceed directly to step three.
The time required for the installation of these changes at a steam
electric powerplant, for example, will vary from as low as 3-4 months
for the modification of an individual screen bay to as much as two years
to completely construct a new intake.
Cost of Implementation of Intake Structure Technology
The cost of the implementation of the required technology can vary from
intake to intake. The costs associated with implementation will be
mainly due to the capital costs of the facilities proposed. Operation
and maintenance costs are relatively small for existing intakes and the
technology will not increase these costs significantly.
New Intakes
The cost of intake structures at powerplants is presently estimated to
be between $3 and $20 (between 2 and 10% of present plant cost) per
kilowatt of installed capacity, the lower range being for larger
circulation water intakes of the shoreline type. The higher range is
157
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for intakes for smaller service water systems which require extensive
offshore piping.
The potentially major cost-impacting measures would be those that
require a reduced approach velocity ;and the requirement for flush
mounting screens. The implementation of these measures might add as
much as 70% to the cost of a tankside intake. For a powerplant this
would be equivalent to between $2 and $4 per kilowatt of installed
capacity. Installing an offshore intake reather than a bankside intake
can add considerably more to the cost.
Existing Intakes
The cost impact to existing sources can be considerably greater than to
new sources. In the worst case, where an entirely new intake is
required which requires extensive offshore conduit, the cost should be
as great as the $20 per kilowatt stated above. The impact of this cost
on an older plant will generally be more severe than on a newer plant.
Since these changes cannot be entirely relied upon to actually reduce
adverse environmental impact in any case, these modifications should be
carefully considered before implementation.
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SECTION VIII
ACKNOWLEDGEMENTS
The development of this report was accomplished through the efforts of
Burns and Roe, Inc. The following Burns and Roe, Inc., technical staff
members made significant contributions to this effort:
Henry Gitterman, Director of Engineering
John L. Rose, Chief Environmental Engineer
Arnold S. Vernick, Project Manager
William A. Foy, Senior Environmental Engineer
Richard T. Richards, Supervising Civil Engineer
The actual preparation of this document was accomplished through the
efforts of the secretarial and other non-technical staff members at
Burns and Roe, Inc., and the Effluent Guidelines Division. Significant
contributions were made by the following individuals:
Ms. Sharon Ashe, Effluent Guidelines Division
Ms. Brenda Holmone, Effluent Guidelines Division
Ms. Chris Miller, Effluent Guidelines Division
Ms. Marilyn Moran, Burns and Roe, Inc.
Ms. Kaye Starr, Effluent Guidelines Division
Mr. Edwin L. Stenius, Burns and Roe, Inc.
The contributions of Ernst P. Hall, Deputy Director, Effluent Guidelines
Division, and C. Ronald McSwiney, Effluent Guidelines Division, were
vital to the timely publication of this report. Ms. Kir Krickenberger
and Dr. Chester Rhines of the Effluent Guidelines Division also assisted
in the preparation of rhis report.
The members of the working group/steering committee, who coordinated the
internal EPA review, in addition to Mr. Cywin and Dr. Nichols are:
Walter J. Hunt, Chief, Effluent Guidelines Development Branch, EGD
Dr. Clark Allen, Region VI
Alden G. Christiansen, National Environmental Research
Center, Corvallis
Swepe Davis, Office of Planning and Management
Don Goodwin, Office of Air Quality Planning and Standards
William Jordan, Office of Enforcement and General counsel
Charles Kaplan, Region IV
Steve Levy, office of Solid Waste Management Programs
Harvey Lunenfeld, Region II
George Manning, Office of Research and Development
Taylor Miller, Office of General Counsel
James Shaw, Region VIII
James Speyer, Office of Planning and Management
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Howard Zar, Region V
Other EPA and State Personnel contributing to this effort are:
Allan Abramson, Region IX
Ken Bigos, Region IX
Carl W. Blomgren, Region VII
Danforth G. Bodien, Region X
Richard Burkhalter, State of Washington
Gerald P. Calkins, State of Washington
Robert Chase, Region I
William Dierksheide, Region IX
William Eng, Region I
James M. Gruhlke, Office of Radiation Programs
William R. Lahs, Office of Radiation Programs
Don Myers, Region V
Dr. Guy R. Nelson, National Environmental Research Center,
Corvallis
Courtney Riordan, Office of Technical Analysis
William H. Schremp, Region III
Edward Stigall, Region VII
Dr. Bruce A. Tichener, National Environmental Research
Center, Corvallis
Srini Vasan, Region V
Other Federal agencies cooperating are:
Atomic Energy Commission
National Marine Fisheries Service, National Oceanographic
and Atmospheric Administration, Department of Commerce
Bureau of Reclamation, Department of the Interior
Bureau of Sport Fish and Wildlife, Department of the Interior
Tennessee Valley Authority
The Environmental Protection Agency also wishes to thank the repre-
sentatives of the steam electric generating industry, including the
Edison Electric Institute, the American Public Power Association and the
following utilities and regional systems for their cooperation and
assistance in arranging plant visits and furnishing data and
information.
Alabama Power Company
Canal Electric Company
Central Hudson Gas & Electric Corporation
Commonwealth Edison Company
Consolidated Edison Company of New York, Inc.
Consumers Power Company
Duke Power Company
Florida Power & Light Company
Fremont, Nebraska Department of Utilities
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MAPP Coordination center for the Mid-Ccntinent
Area Power Systems
New England Power company
New York Power Pool
New York State Electric & Gas Corporation
Niagara Mohawk Power corporation
Omaha Public Power District
Pacific Gas & Electric company
Pacific Power & Light Company
Pennsylvania Power & Light Company
Portland General Electric Company
Potomac Electric Power company
Public Service Company of Colorado
Public Service Electric & Gas company
Sacramento Municipal Utility District
Southern California Edison company
Taunton, Massachusetts Municipal Light Plant
Texas Electric Service company
Virginia Electric & Power Company
Acknowledgement is also made to the following manufacgurers for their
willing cooperation in providing information needed in tne course of
this effort.
Beloit-Passavant
F. W. Brackett & Company, Ltd.
J. Blakeborough & Sons, Ltd.
Link Belt Company
R. E. Reimund Company
Rexnord, Inc.
Stephens-Adamson
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SECTION IX
KEFERENCES
1. Bates, D.W., Diversion, and Collection of Juvenile Fish wirh
Traveling Screens, U.S. Department of the Interior, Fishery
Leaflet 633, (March 1970).
2. Beall, S. E., Us§_s_of_Waste_Heat, research sponsored by
the U.S. AEC under contract with the Union Carbide
Corporation, (November 3, 1969).
3. "Director", Public Power, Vol. 31, No. 1, (January -
February 1973).
4. "Dive Into Those Intakes", Electric_Lic[ht_&_Power, E/G
edition, pp. 52-53, (November 1972) .
5. Electric Power .Statistics, Federal Power Commission,
(January 1972).
6. Electrical World^ Directgry_of_Electric Utilities, McGraw-Hill
Inc., New York, 31st Edition, (1972-1973).
7. Environmental Effects of Producing Electric Power Hearings
before the Joint Committee on Atomic Energy 91st congress,
Second Session, Parts 1 and 2, Vol. I & II, (October, November
1969 and January and February 1970).
8• Final Environmental Statement, USAEC, Directorate of Licensing:
a) Arkansas Nuclear One Unit 1
Arkansas Power & Light Co., (February 1973).
b) Arkansas Nuclear One Unit 2
Arkansas Power & Light Co., (September 1972).
c) Davis-Bessee Nuclear Power Station
Toledo Edison company 6 Cleveland Electric
Illuminating Company, (March 1973).
d) Duane Arnold Energy Center
Iowa Electric Light & Power Company
Central Iowa Power Cooperative
Corn Belt Power Cooperative, (March 1973) .
e) Enrico Fermi Atomic Power Plant Unit 2
163
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Detroit Edison Company, (July 1972).
f) Fort Calhoun Station Unit 1
Omaha Public Power District, (August 1972).
g) Indian Point Nuclear Generating Plant UNit No. 2
Consolidated Edison Co. of New York, Inc., Vol. 1
(September 1972).
h) Indian Point Nuclear Generation Plant Unit No. 2
Consolidated Edison Co. Of New York, Inc. Vol. II
i) James A. Fitzpartrick Nuclear Power Plant
Power Aurthority of the State of New York,
(March 1973).
j) Joseph M. Farely Nuclear Plant Units 1 and 2
Alabama Power Company, (June 1972).
k) Kewaunee Nuclear Power Plant
Wisconsin Public Service Corporation,
(December 1972).
1) Maine Yankee Atomic Power Station
Maine Yankee Atomic Fewer Company, (July 1972) .
m) Oconee Nuclear Station Units 1, 2 and 3
Duke Power company, (March 1972).
n) Palisades Nuclear Generating Plant
Consumers Power Company, (June 1972).
o) Pilgrim Nuclear Power Station
Boston Edison Company, (May 1972).
p) Point Beach Nuclear Plant Units 1 and 2
Wisconsin Electric Power Co. and
Wisconsin Michigan Power Company, (May 1972).
q) Quad-Cities Nuclear Power Station Units 1 and 2
Commonwealth Edison Company and the
Iowa-Illinois Gas and Electric Company,
(September 1972) .
r) Rancho Seco Nuclear Generating Station Unit 1
Sacramento Municipal Utility District, (March 1973)
s) Salem Nuclear Generating Station Units 1 and 2
Public Service Gas & Electric Company, (April 1973)
164
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t) Surry Power Station Unit 1
Virginia Electric and Power Co., (May 1972).
u) Surry Power Station Unit 2
Virginia Electric & Power Co. (June 1972).
v) The Edwin I. Hatch Nuclear Plant Unit 1 and 2
Georgia Power company, (October 1972).
w) The Fort St. Vrain Nuclear Generating Station
Public Service company of Colorado, (August 1972) .
x) Three Mile Island Nuclear Station Units 1 and 2
Metropolitan Edison Company, Pennsylvania Electric
Company and, Jersey Central Power and Light Co.,
(December 1972).
y) Turkey Point Plant
Florida Power and Light Co., (July 1972).
z) Vermont Yankee Nuclear Power Station
Vermont Yankee Nuclear Power Corporation, (July 1972).
aa) Virgil C. Summer Nuclear Station Unit 1
South Carolina Electric £ Gas Company, (January 1973) .
bb) William B. McGuire Nuclear Station Units 1 and 2
Duke Power company, (October 1972).
cc) Zion Nuclear Power Station Units 1 and 2
Commonwealth Edison Company, (December 1972).
9. Garton, R. G. and Harkins, R. D., Guidelines: Biological
Surveygmat Proposed Heat Discharge Sites EPA Water Quality
Office, Northwest Region. (April 1970).
10. Hirayama, K., and Hirano, R., "Influence of High Temperature
and Residual Chlorine on Marine Phytoplankton".
11. Intake Systems for Desalting Plants, U.S. Department of
Interior, Office of Saline Water, Research and Development
Progress Report No. 678, (April 1971) .
12. Jenson, L.D. and Brady, O.K., "Aquatic Erosystems and
Thermal Power Plants". Proceedings of the ASCE,
(January 1971) .
13. Maxwell, W.A., Fish Diversion for Electrical Generating
Station Coolinc Systems - A State^of the Art Report, for
Florida Power & Light Co., (March 1973) .
165
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14. Mayo, R.D. and James W.T., "Rational Approach to the Design
of Power Plant Intake Fish Screens using both Physical
and Behavioral Screening Methods", Technical Reprint
No. 15, Kramer, Chin & Mayo, (September 1972).
15. Metric^Practice Guide, (A Guide to the Use of Si - the Inter-
national System of Units), American Society for Testing and
Materials, Philadelphia, Pennsylvania.
16 Peterson, D.E., Sonnichsen, Jr., et al, "Thermal Capacity
of Our Nation's Waterways", ASCE Annual & National
Environmental Engineering Meeting, (October 1972).
17. Report on Best Intake Technology Available for Lake
Michigan, Preliminary Draft, by Ccoling Water Intake
Technical Committee, (May 1973).
18. Richards, R.T., "Fish Protection at Circulating Water Intake",
Burns and Roe, Inc., unpublished research paper. May 11, 1967.
19. Richards, R.T. , Intake for the Makeup Water Pumping System
WPPSS tjuclear Project No., 2 prepared for Washington Public
Power Supply System, (March 1973).
20. Richards, R.T. , "Intake for the Makeup Water Pumping System,
Hanford No. 2", Burns and Roe, Inc., (January 1973).
21. Riesbal, H.S. and Gear, R.J.L., "Application of Mechanical Systems
to Alleviation of Intake Entrapment Problems", presented at the
Atomic Industrial Forum, Conference on Water Quality Considerations,
Washington, D.C., (October 2, 1972).
22. Schreiber, D.L., et al, Appraisal of Water Intake Systems
on the Central CQlumbia_River to Washington Public Power
Supply~System (March 1973).
23. Skrotzki, E.G.A. and Vopat, W.A., Power Station Engineering
and Economy, McGraw Hill Book Co., N.Y. (1960).
24. Sonnichsen, Jr., J.C., Bentley, B.W., et al, A Review of
Thermal Power Plant Intake Structure Designs and Related
Environmental Considerations prepared for the U.S. Atomic
Energy Commission, Division of Reactor Development and
Technology.
25. Statistics of Privately Owned Electric .Utilities of the U.S. -
1970, Federal Power Commission, (December 1971).
166
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26. Statistics of^Publicly^Owned,Electric ^Utilities of_the U.S. -
1970, Federal Power commission, (February 1972).
27. steanL^^c^ric_PlantA_Air_and_Viater_fiualitx_Controlf Summary
Report, Federal Power Commission, (December 1969).
28. ^t^gni_Kl_££h£ic_Plant_Construction Cost and Annual Production
Expenses, Twenty-Second Annual Supplement, Federal Power
Commission, (1969).
29. The_Electricity_Su£p.ly_Industry., 22nd Inquiry, The
Organization for Economic Co-operation and Development (1972).
30. Bibko, P., et al, "Effects of Light and Bubbles on tne Screening
Behavior of the Striped Bass", westinghcuse Environmental
Systems, paper presented at the Entrainment and Intake
Screening Workshop, ;the Jchn Hopkins University,
(February 8, 1973) .
31. Skinner, J.E., California Department of Fish and Game,
"Evaluation of Large Functional Louver Screening Systems
and Fish Facilities, Research on California Water
Diversion Projects", paper presented at the Entrainment
and Intake Workshop, the John Hopkins University,
(February 8, 1973) .
32. Schuler, V.J. and Larson, L.E., Ichthyological Associates
and Southern California Edison Company, Fish Guidance and
Louver Systems at Pacific Ccast Intake Systems", paper
presented at the Entrainment and Intake Workshop, The
John Hopkins University, (February 8, 1973) .
33. Beloit-Passavant_CorporatiQn_Bulletin_1100
34. Engineering^!:or Resolution of the Energy - Environment Dilemma,
Committee on Power Plant Siting, National Academy of
Engineering, Washington, D.C., (1972).
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SECTION X
GLCSSAEY
Agglomeration
The coalescence of dispersed suspended matter into larger floes or
particles which settle more rapidly.
Brackish Water
Water having a dissolved solids content between that of fresh water and
that of sea water, generally from 1000 to 10,000 mg per liter.
Brine
Water saturated with a salt.
CFM
Cubic foot (feet) per minute.
Circulating Water_Pumps
Pumps which deliver cooling water to the condensers of a powerplant.
Circulating__Water_ System
A system which conveys cooling water from its source to the main
condensers and then to the point of discharge. Synonymous with cooling
water system.
Closed Circulating Water System
A system which passes water through the condensers, then through an
artificial cooling device, and keeps recycling it.
Cooling Canal
A canal in which warm water enters at one end, is cooled by contact with
air, and is discharged at the other end.
Cooling^ Lake
See Cooling Pond.
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Cooling Pond
A body of water in wnich warm water is cooled by contact with air, and
is either discharged cr returned for reuse.
Cooling Tower
A h^t exchange device which transfers reject heat from circulating
water to the atmosphere.
Cooling Water System
See Circulating Water System.
Crib
A type of inlet structure.
Critical Aguatic Organisms
Aquatic organisms that are commercially or recreationally valuable, rare
or endangered, of specific scientific interest, or necessary to the
well-being of some significant species or to the balance of the
ecological system.
Curtain Wall
A vertical wall at the entrance to a screen or intake structure
extending from above, to some pcint below, the water surface.
To release or vent.
Discharge Pipe or Conduit
A section of pipe or conduit from the condenser discharge to the point
of discharge into receiving waters or cooling device.
Entrair.ment
The drawing along of organisms due to the mass motion of the cooling
water.
Entrapment
The prevention of the escape of organisms due to the cooling water
currents and forces involved.
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Fiiter_Bed
A device for removing suspended sclids from water, consisting of
granular material placed in horizontal layers and capable of being
cleaned hydraulically by reversing the direction of the flow.
Filtration
The process of passing a liquid through a filtering medium for the
removal of suspended or colloidal matter.
Fixed or Stationary Screen
A nonmoving fine mesh screen which must be lifted out of the waterway
for cleaning.
Floe
Small gelatinous masses formed in a liquid by the reaction of a
coagulant added thereto, thru biochemical processes, or by
agglomeration.
FPS
Foot (feet) per second
Foot (feet) - Designated as 11, 21 , etc.
Impingement
Sharp collision of organism with a physical member of the intake
structure.
ID
Inside diameter
Inch (inches)
Designated as 1", 2", etc.
Infiltration Bed
A device for removing suspended solids from water consisting of natural
deposits of granular material under which a system of pipes collect the
water after passage through the bed.
Inlet Pipe or Conduit
See Intake Pipe or Conduit.
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Intake_Pi2§_2£_ conduit
A section of pipe or conduit from the pump discharge to tne condenser
inlet; also used for the pipe leading from the inlet to the screens or
pumps.
Intake or_Intak,e_Structure
A structure containing inlet, water cleaning facilities and/or pumps.
KN
Kilo Newton
MPS
Meters per second.
Makeup Water_Pump_s
Pumps which provide water to replace that lost by evaporation, seepage,
and blowdown.
Mine-mouth_Plant
A steam electric powerplant located within a short distance of a coal
mine and to which the coal is transported from the mine by a conveyor
system, slurry pipeline or truck.
M3
Cubic Meter
Nominal Capacity
Name plate - design rating of a plant, or specific piece of equipment.
Once-through Circulating Water System
A circulating water system which draws water from a natural source,
passes it through the main condensers and returns it to a natural body
of water.
Powerplant
Equipment that produces electrical energy, generally be conversion from
heat energy produced by chemical or nuclear reaction.
Pump and_Screen_Structure
A structure containing pumps and facilities for removing debris from
water.
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Pump Chamber
A compartment of the intake or pump and screen structure in which the
pumps are located.
Pump Runout
The tendency of a centrifugal pump to deliver more than its design flow
when the system resistance falls below the design head.
PVC
Polyvinylchloride
Recirculation System
Facilities which are specifically designed to divert the major portion
of the cooling water discharge back to the cooling water intake.
Recirculation
Return of cooling water discharge back to the cooling water intake.
Salin e_ Water
Water containing salts.
Second
Abbreviation = s
Sampling, Stations
Locations where several flow samples are tapped for analysis.
Screen Chamber
A compartment of the intake of pump and screen structure in which the
screens are located.
Screen Structure
A structure containing screens for removing debris from water.
Sedimentation
The process of subsidence and deposition of suspended matter carried by
a liquid.
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Service Water Pumps
Pumps providing water for auxiliary plant heat exchangers ana other
uses.
Station
A plant comprising one or several units for the generation of power.
Stop Logs
A device inserted in guides at the entrance to a waterway to permit
dewatering. It can be made up of individual timber logs, but more
commonly of panels of steel, timber, or timber and concrete.
Total Dynamic Head ITDH]_
Total energy provided by a pump consisting of the difterence in
elevation between the suction and discharge levels, plus losses due to
unrecovered velocity heads and friction.
Tgg§h_Ragk^ Trash gars. Grizzlies
A grid, coarse screen or heavy vertical bars placed across a water inlet
to catch floating debris.
Trash Rake
A mechanism used to clean the trash rack.
Traveling^Screen
A device consisting of a continuous band of vertically or nearly
vertically revolving screen elements placed at right angles to tne water
flow. Screen elements are cleaned automatically at the tope of the
revolution.
Turbidity
Presence of suspended matter such as organic or inorganic material,
plankton or other microscopic organisms which reduce the clarity of the
water.
Unit
In steam electric generation, the basic system for power generation
consisting of a boiler and its associated turbine and generator with the
required auxiliary equipment.
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Utili-t-y
(Public utility) a company, either investor-owned or publicly owned
which provides service to the public in general. The electric utilities
generate and distribute electric power.
Velocity Cap, Fish Cap
A horizontal plate placed over a vertical inlet pipe to cause flow into
the pipe inlet to be horizontal rather than vertical.
Wet Well
A compartment of the pump structure in which the liquid is collected and
to which the pump suction is connected.
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